DB2 Reference.doc

Table Of Contents

1. PURPOSE AND SCOPE OF THE DOCUMENT.................................................1

1.1. USERS OF THE DOCUMENT...............................................................................11.2. ASSOCIATED DOCUMENTS................................................................................1

2. INTRODUCTION................................................................................................... 2

2.1. DATABASE MANAGEMENT SYSTEMS (DBMS)..................................................32.2. TYPES OF DBMS............................................................................................. 4

2.2.1. Relational DBMS.................................................................................... 42.2.2. HIERARCHICAL DBMS.........................................................................62.2.3. Net Work DBMS...................................................................................... 7

2.3. SAMPLE DB2 DATABASE..................................................................................8

3. STRUCTURE OF DB2...........................................................................................9

3.1. HIERARCHY OF DATA STRUCTURES.................................................................93.2. DATABASES...................................................................................................... 93.3. DB2 STORAGE GROUPS.................................................................................... 93.4. TABLE SPACES................................................................................................. 9

3.4.1. Simple Tablespace................................................................................... 93.4.2. Segmented Table Space...........................................................................93.4.3. Partitioned Table Space..........................................................................9

3.5. TABLES............................................................................................................ 93.6. INDEX SPACES.................................................................................................. 93.7. INDEXES........................................................................................................... 93.8. VIEWS.............................................................................................................. 93.9. SYNONYMS...................................................................................................... 93.10. ALIASES........................................................................................................... 93.11. DB2 CATALOG................................................................................................. 93.12. DB2 DIRECTORY.............................................................................................. 93.13. ACTIVE AND ARCHIVE LOGS............................................................................93.14. BUFFER POOLS................................................................................................. 9

4. DATA TYPES........................................................................................................ 39

4.1. NUMERIC DATA.............................................................................................. 394.1.1. Nulls..................................................................................................... 39

4.2. STRING DATA................................................................................................. 394.3. CHARACTER FORMAT.....................................................................................394.4. DATE/TIME DATA...........................................................................................394.5. EQUIVALENT COBOL DECLARATIONS OF DATA TYPES....................................39

5. SQL PROGRAMMING.......................................................................................49

5.1. DDL STATEMENTS.......................................................................................... 515.1.1. Create Database...................................................................................515.1.2. Create Table Space...............................................................................515.1.3. Create Table.......................................................................................... 515.1.4. Create View........................................................................................... 515.1.5. Create Index.........................................................................................515.1.6. Alter Table............................................................................................515.1.7. Drop..................................................................................................... 51

©Case Consult (India) Pvt. Ptd. 03/1998 DB2 Fundamentals

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5.2. DML STATEMENTS.........................................................................................645.2.1. Select.................................................................................................... 645.2.2. Joining Tables....................................................................................... 645.2.3. Sub Queries..........................................................................................645.2.4. Union.................................................................................................... 645.2.5. Insert.................................................................................................... 645.2.6. Update.................................................................................................. 645.2.7. Delete................................................................................................... 64

5.3. CONTROL STATEMENTS..................................................................................825.3.1. Grant.................................................................................................... 825.3.2. Revoke.................................................................................................. 825.3.3. Commit................................................................................................. 825.3.4. Roll Back.............................................................................................. 82

6. PROGRAM STRUCTURE..................................................................................87

6.1. HOST VARIABLES........................................................................................... 876.1.1. Declaring Host Variables......................................................................87

6.2. INDICATOR VARIABLES...................................................................................876.3. SQLCA.......................................................................................................... 876.4. COBOL STRUCTURE OF SQLCA.....................................................................876.5. SQLCA RETURN CODES................................................................................876.6. SQLCA WARNINGS........................................................................................ 876.7. IMPORTANT SQL CODES.................................................................................876.8. STATIC SQL................................................................................................... 876.9. DYNAMIC SQL............................................................................................... 876.10. EXAMPLE FOR A DB2 APPLICATION PROGRAM..............................................87

7. PROGRAM PREPARATION............................................................................122

7.1. STEPS IN PROGRAM PREPARATION................................................................1227.2. DCLGEN (DECLARATIONS GENERATOR )......................................................1227.3. PRECOMPILE................................................................................................. 1227.4. BIND............................................................................................................ 122

7.4.1. Binding A DBRM To A Package..........................................................1227.4.2. Binding An Application Plan..............................................................122

7.5. COMPILE AND LINKEDIT...............................................................................1227.6. OVERVIEW OF DB2 APPLICATION PROGRAM PREPARATION AND EXECUTION

1227.7. ASSOCIATING LOAD MODULES AND PACKAGES...........................................122

8. SECURITY FEATURES....................................................................................140

8.1. PRIVILEGES.................................................................................................. 1408.2. REFERENTIAL INTEGRITY..............................................................................140

8.2.1. DB2 Enforcement Of Referential Integrity..........................................1408.2.2. Referential Integrity Enforcement Rules..............................................1408.2.3. Example For Referential Integrity Violation.......................................140

8.3. DATABASE RECOVERY IN CASE OF FAILURE................................................1408.3.1. Unit Of Recovery................................................................................1408.3.2. Data Recovery....................................................................................140

9. CONCURRENCY............................................................................................... 157

9.1. CONCURRENCY............................................................................................1579.2. LOCKING STRATEGY.....................................................................................157



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9.3. LOCK SIZES AND TYPES...............................................................................1579.4. ACQUIRE RELEASE PARAMETERS.................................................................1579.5. ISOLATION PARAMETER................................................................................157

10. DB2I (DB2 INTERACTIVE )........................................................................167

10.1. DB2I............................................................................................................ 16710.2. SPUFI.......................................................................................................... 167

11. UTILITIES..................................................................................................... 171

11.1. LOAD........................................................................................................... 17111.2. RUNSTATS..................................................................................................... 17111.3. REORG......................................................................................................... 171

12. ADVANCED DB2........................................................................................... 179

12.1. MORE ABOUT INDEXES................................................................................17912.1.1. Example Of An Index..........................................................................17912.1.2. Clustered Indexes................................................................................17912.1.3. Non Clustered Indexes........................................................................179

12.2. SPECIAL REGISTERS...................................................................................... 17912.3. MORE ABOUT LOCKS...................................................................................179

12.3.1. Modes Of Table And Tablespace Locks...............................................17912.3.2. Modes Of Row And Page Locking.......................................................17912.3.3. Lock Mode Compatibility Of Table And Table Space Locks.................17912.3.4. Lockmode Compatibility Of Row And Page Locks..............................179

12.4. Invoking Online Utilities.............................................................................179



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1. Purpose and Scope of the Document

The Purpose of this document is to train fresh Software Engineers who would like to get familiarised with DB2 and as a reference material for application programmers.

1.1. Users of the Document

This document is intended for database designers, database application programmers, students and teachers and more generally anyone who wishes to broaden his or her knowledge of the database, DB2.

1.2. Associated Documents

No associated documents

2. Introduction

DB2 ( IBM DATABASE2 ) is a highly successful relational database management system. DB2 enables it’s users to create, update and control relational database using STRUCTURED QUERY LANGUAGE (SQL). Designed to meet the needs of small and large business alike, DB2 is available on a number of platforms. we will be dealing with DB2 on MVS.

RISC SYSTEM/6000

DB2 FORDB2 FOR OS/2

AIX

DB2 FOR DB2 FOR DB2 FOR HP-UX SOLARIS WINDOWS /NT

DB2 FOR SINIX

DB2 FOR MVS DB2 FOR

OS/400

DB2 FORVSE & VM

2.1. Database Management Systems (DBMS)

DATABASE MANAGEMENT SYSTEMS deal with the problem of storing and retrieving large amounts of data. DBMS provides an environment to share data among it’s users. Preserving the correctness of data and restoring the database in failure are major concerns for DBMS.

DBMS

DBMS CONSIST OF DATA, HARDWARE, SOFTWARE AND USERS BENEFITS OF DBMS ARE

REDUCE REDUNDANCY AVOID INCONSISTENCY SHARE DATA MANIPULATES DATA EFFICIENTLY FAULT TOLERANT DATA INDEPENDENCE

DATA

DATABASE

APPLICATION PROGRAM

QUERY PROCESSOR

STORAGE MANAGER

2.2. Types Of DBMS

Depending on data models used, database management systems are mainly divided into three.

RELATIONAL DBMS HIERARCHICAL DBMS NETWORK DBMS

2.2.1.Relational DBMS

DB2 is based on relational data model which was formulated by DR. E.F CODD in 1970. Relational systems have their origin in the mathematical theory of relations. Using relational data model , IBM developed DB2 in 1983.

A RELATIONAL SYSTEM IS A SYSTEM IN WHICH

THE DATA IS PERCEIVED BY THE USER AS TABLES QUERIES ARE USED TO EXTRACT DATA FROM THE DATABASE. ALL DATA VALUES ARE ATOMIC. ie EVERY ROW AND COLUMN

POSITION CONTAINS ONLY ONE DATA VALUE; NEVER A LIST OF VALUES

EXAMPLE OF RELATIONAL DBMS IS DB2

SAMPLE DATABASE FOR COMPARING DIFFERENT DBMS

TABLE S TABLE SP

S# SNAME STATUS CITY S# P# QTY

S1 SMITH 20 LONDON S1 P1 300 S2 JONES 10 PARIS S1 P2 200 S3 BLAKE 30 PARIS S1 P3 400

S2 P1 300 S2 P2 400

TABLE P S3 P2 200

P# PNAME COLOR WEIGHT CITY

P1 NUT RED 12 LONDON P2 BOLT GREEN 17 PARIS P3 SCREW BLUE 17 ROME P4 SCREW RED 14 LONDON

TABLE S represents SUPPLIERS. Each supplier has a unique SUPPLIER NUMBER (S#), a SUPPLIER NAME (SNAME), a RATING (STATUS) and a LOCATION OF THE SUPPLIER (CITY).

TABLE P represents PARTS. Each kind of part has a unique PART NUMBER (P#), a PART NAME (PNAME), a COLOUR (COLOR), a WEIGHT (WEIGHT) and a location where the PART IS STORED (CITY).

TABLE SP represents SHIPMENTS. It connects other two tables. It REPRESENTS a shipment of parts of kind P1 by the supplier called S1 and the shipment quantity.

In a relational data model TABLES are called RELATIONS, ROWS are called TUPLES and COLUMNS are referred as ATTRIBUTES.

In a relational data mode association of ROWS of different TABLES are done using COLUMN VALUES of common columns.

DB2 relates TABLE S and SP using the COLUMN SUPPLIER NUMBER(S#). TABLE P and SP are related using the COMMON attribute PART NUMBER (P#). TABLES S and P are related using COLUMN (CITY)

2.2.2. HIERARCHICAL DBMS

Hierarchical View Of Supplier And Parts Database

In hierarchical database suppliers, parts and shipments are different databases

SUPPLIERS DATABASE PARTS DATABASE

S1 P1S2 …..

SMITH NUT

JONES

20 RED 12 LONDON10

LONDON SHIPMENTS DATABASE

PARIS SHIPMENT SEGMENT

LCHILD

In this view data is represented by a simple TREE STRUCTURES and DBMS links these data bases using pointers.

The user sees three individual trees for supplier database, each tree has a parent supplier. Each tree can be called a supplier record occurrence. Similarly you can see part record occurrence and shipment record occurrence.

Shipment database contains the shipment quantity. The logical child of shipment database consists of supplier number , part number and pointers to corresponding databases .Similarly the supplier and parts databases also contains logical child which points to the shipment database. Now the user can access shipment from supplier and part databases. Similarly parts and supplier databases are also accessed from shipment database

IMS (Information management system) is an example of Hierarchical DBMS

2.2.3. Net Work DBMS

SUPPLIER PART RECORDRECORD SET SET

S1 SMITH….. P1 NUT …..

S2 JONES….. P2 BOLT…….

QUANTITY RECORDS

300

400

…….

NETWORK DBMS consists of owner databases and member databases. The member database can be accessed only via the owner database.

In the example there are two owners for a member database. Supplier and part record sets are owners of shipment record set. Using this database the user can access the shipment of a particular part by a specific supplier

The supplier S1 supplies part P1 of quantity 300. From the supplier S1 there is a pointer towards the supplied quantity and another pointer connects this to the corresponding part. An owner can have more than one pointer towards different quantities.

Example of network database is IDMS(Integrated database management system)

2.3. Sample Db2 Database

The sample database consists of THREE tables and these tables are used through out this book.

TABLE S TABLE SP


S1 SMITH 20 LONDON S1 P1 300 S2 JONES 10 PARIS S1 P2 200 S3 BLAKE 30 PARIS S1 P3 400 S4 CLARK 20 LONDON S1 P4 200 S5 ADAMS 30 ATHENS S1 P5 100

S1 P6 100 S2 P1 300

TABLE P S2 P2 400 S3 P2 200

P# PNAME COLOR WEIGHT CITY S4 P2 200 S4 P4 300

P1 NUT RED 12 LONDON S4 P5 400 P2 BOLT GREEN 17 PARIS P3 SCREW BLUE 17 ROME P4 SCREW RED 14 LONDON P5 CAM BLUE 12 PARIS P6 COG RED 19 LONDON

TABLE S represents SUPPLIERS. Each SUPPLIER has a unique SUPPLIER NUMBER (S#), a SUPPLIER NAME (SNAME), a RATING (STATUS) and a location of the SUPPLIER (CITY). PRIMARY KEY IS S#.

TABLE P represents PARTS. Each kind of part has a unique PART NUMBER (P#), a PART NAME (PNAME), a COLOUR (COLOR), a WEIGHT (WEIGHT) and a LOCATION where the PART IS STORED (CITY).

PRIMARY KEY IS P#

TABLE SP represents SHIPMENTS .It connects other TWO TABLES .It represents a SHIPMENT of PARTS OF KIND P1 by the SUPPLIER called S1 and the SHIPMENT QUANTITY. For a given SHIPMENT the combination of S# and P# is unique .That is the PRIMARY KEY is the COMBINATION of the above mentioned and the FOREIGN KEYS ARE S# AND P#

3. Structure Of DB2

This chapter deals with the definitions and examples of objects present in DB2.The topics included in this chapter are

3.1. Hierarchy Of Data Structures

3.2. Databases

3.3. DB2 Storage Groups

3.4. Table Spaces

3.4.1. Simple Tablespace

3.4.2. Segmented Table Space

3.4.3. Partitioned Table Space

3.5. Tables

3.6. Index Spaces

3.7. Indexes

3.8. Views

3.9. Synonyms

3.10. Aliases

3.11. DB2 Catalog

3.12. DB2 Directory

3.13. Active And Archive Logs

3.14. Buffer Pools

STRUCTURE OF DB2

THE ELEMENTS OF DB2 ARE DIVIDED INTOTWO BROAD CATEGORIES

DATA STRUCTURES SYSTEM STRUCTURES

DATA STRUCTURES CONTAIN USER DATA AND ARE ACCESSEDUNDER USER’S DIRECTION.

SYSTEM STRUCTURES ARE CONTROLLED AND ACCESSED BY DB2

DATA STRUCTURES CONSIST OF DATABASES DB2 STORAGE GROUPS TABLE SPACES TABLES INDEX SPACES INDEXES VIEWS SYNONYMS ALIASES

SYSTEM STRUCTURES MAINLY CONSIST OF

DB2 CATALOG DB2 DIRECTORY ACTIVE AND ARCHIVE LOGS BUFFER POOLS

HIERARCHY OF DATA STRUCTURES

DATABASE D1

TABLE SPACE S1

TABLE T1 TABLE T2

INDEX X1

INDEX X2

TABLE T3 PARTITIONED PART 1 TABLESPACE S2 TABLE T3 PART 2

PARTITIONED INDEX X3 PART 1

PARTITIONED INDEX X3 PART 2

STORAGE GROUP G1

VOLUME 1 (DASD)

VOLUME 2 (DASD)

STORAGEGROUP G2

VOLUME2 (3380)

Hierarchy Of Data structures

The total collection of stored data is divided into a number of disjoint databases. They are USER DATABASES and SYSTEM DATABASES.

Each database is divided into a number of disjoint ‘spaces’, that is several TABLESPACES and INDEX SPACES. A space is a dynamically extendible collection of PAGES, where PAGE is a block of physical storage.

Each table space contains one or more stored tables. A stored table contains a set of stored records. A given stored table must be wholly contained within a single table space.

Each INDEXSPACE contains exactly one index. A given index must be wholly contained with in a single index space. A given stored table and all of its associated indexes must be wholly contained within a single DATABASE.

Each space (TABLE SPACE or INDEX SPACE) has an associated STORAGE GROUP. When a space needs to be extended, storage is acquired from appropriate storage group.

DATA BASES

DATABASE1

DATABASE IS A COLLECTION OF A NUMBER OF TABLE SPACES ALONG WITH A SET OF INDEX SPACES

A STORED TABLE AND ALL OF IT’S ASSOCIATED INDEXES MUST BE IN A SINGLE DATABASE

WHEN YOU CREATE A TABLESPACE OR TABLE AND DO NOT SPECIFY THE DATABASE THE OBJECT WILL BE CREATED IN THE DEFAULT

DATABASE DSNDB04

TABLESPACE1

INDEX 1 TABLE 1 TABLE 2

INDEX 2

TABLESPACE 2

DB2 STORAGE GROUPS

STORAGE GROUP 1

USER AND SYSTEM DATABASES ARE PHYSICALLY STORED IN THE DATASETS OF SPECIFIED STORAGE GROUPS

STORAGE GROUP IS A SET OF VOLUMES OF DIRECT ACCESS STORAGE DEVICES(DASD).

PARTS OF SINGLE DATABASE CAN BE STORED IN DIFFERENT STORAGE GROUPS

DEFAULT STORAGE GROUP IS SYSDEFLT

VOLUME 1 VOLUME 2

TABLE SPACES

TABLESPACE 1

SIMPLE SEGMENTED PARTITIONED

TABLESPACE IS MADE UP OF ONE OR MORE VSAM LINEAR DATASETS

(LDS ), WHERE ONE OR MORE TABLES ARE STORED.

A TABLE SPACE IS DIVIDED INTO 4K OR 32K PAGES.

A PAGE IS A UNIT OF I/O TRANSMISSION.

A PAGE MAY CONTAIN ONE OR MORE ROWS (MAX 127).

A ROW MUST LIE WITHIN A PAGE.

TABLE 1

TABLE 2

Table Spaces

A TABLE SPACE can be thought of as a logical address space on secondary storage that is to hold one or more stored tables. Table spaces are divided into equal sized units called PAGES which are written or read from DASD. Tables are physically stored in one or more VASM linear datasets.

A table space can consists of 1 to 64 VSAM datasets which can together contain up to 64 GIGABYTES of data. When you create a table space you can specify the database and storage group to which the tablespace belongs and table space type. As the amount of data in tables grow storage will be acquired from appropriate storage groups and added to the tablespace.

Fundamentally the table space is a storage unit for recovery and reorganization. If the table space is very large the RECOVERY and REORGANIZATION could take a long time. Hence making the tablespace simple, segmented, or partitioned can drastically affect the performance.

SIMPLE TABLESPACE

SIMPLE TABLESPACE

FREE PAGE

FREE SPACE

4KPAGE

RECORD OF TABLE 1

RECORD OF TABLE 2

SIMPLE TABLESPACE CONTAINS ONE OR MORE TABLES

RECORDS OF DIFFERENT TABLES ARE STORED IN AN INTERLEAVED MANNER.

IMPROVE ACCESS TIME FOR LOGICALLY RELATED DATA

Simple Tablespace

In simple table space records of tables are interleaved .Records of different tables may be present in a single page and to find all rows of a table a scan of the whole table space is needed. But by loading the data in an appropriately interleaved manner; accessing logically related data will be more efficient.

If a table is dropped, its rows are not deleted. The space occupied by the rows does not become available until the table space is reorganized. All tables in a simple table space must reside in the same user-defined data set or in the same storage group.

one stored table per table space is always the most satisfactory arrangement in the case of simple TABLE SPACE.

SEGMENTED TABLESPACE

SEGMENT1

SEGMENT2

4K PAGE SEGMENT3

TABLE SPACE HAVING A SEGMENT SIZE 4

RECORD OF TABLE 1

RECORD OF TABLE 2

TABLE SPACE IS DIVIDED INTO A NUMBER OF SEGMENTS.

RECORDS OF DIFFERENT STORED TABLES ARE NOT INTERLEAVED IN A SINGLE SEGMENT.

A SEGMENTED TABLE SPACE CAN CONTAIN ONE OR MORE TABLES.

SEQUENTIAL ACCESS TO A PARTICULAR TABLE IS MORE EFFICIENT.

Segmented Tablespace

In a SEGMENTED TABLESPACE the tablespace is divided into segments and each segment consists of a logically contiguous set of N PAGES. N must be a multiple of 4 in the range 4 TO 64 and is same for all segments in the table space. The size of the segment is specified while creating the tablespace.

Each segment in the segmented tablespace contains rows from only one table. But the tablespace can contain multiple tables, in different SEGMENTS. In order to find a row, it is not necessary to scan the entire table space, but only the segments that contain the table. Hence sequential access to a particular table is more efficient.

If a table in a segmented table space is dropped, the space for that table can be reused without performing a reorganization of the table space.

A segmented table space can have between 1 AND 32 VSAM linear data sets. the maximum size of a data set in the segmented table space is 2 GIGABYTES and so, the maximum size of a segmented table space is 64 GIGABYTES .

PARTITIONED TABLESPACE

A—F PARTITION1

G—P PARTITION2

Q—Z PARTITION3

RECORD OF TABLE 1

A PARTITIONED TABLESPACE CAN CONTAIN ONLY ONE TABLE.

EACH PARTITION CONTAINS A PART OF ONE TABLE.

THE PARTITIONS CAN BE INDEPENDENTLY ASSIGNED TO DIFFERENT STORAGE GROUPS.

IMPROVED DATA AVAILABILITY AND QUERY RESPONSE TIME.

Partitioned Tablespace

PARTITIONED TABLESPACES are intended for stored tables that are sufficiently large. Partitioned table contains exactly one stored table, partitioned in accordance with value ranges of a particular column or column combination .

A partition can be 1, 2, OR 4 GIGABYTES in length, depending on the number of partitions contained in the entire table space. If only one partition is defined on the table space, then its MAXIMUM SIZE IS 4 GIGABYTES.

Partitioning a table space provides several advantages for large tables. When DB2 scans data to answer a query it can scan through partitions simultaneously instead of scanning through the entire table from the beginning to end.

A utility can work on all partitions simultaneously instead of working on one partition at a time. Also, different utilities can work on different partitions simultaneously. This can significantly reduce the amount of time needed for a utility to finish.

TABLES

TABLE S

KEY COLUMNS

S# SNAME STATUS CITY

ROWS S1 SMITH 20 LONDON S2 JONES 10 PARIS S3 BLAKE 30 PARIS S4 CLARK 20 LONDON S5 ADAMS 30 ATHENS

A RELATIONAL DATABASE STORES DATA IN THE FORM OF TABLES.

TABLE CONSISTS OF A NUMBER OF RECORDS.

RECORD CONTAINS COLUMNS, ROWS, KEYS etc.

EACH RECORD SHOULD BE CONTAINED IN A SINGLE PAGE BUT A TABLE CAN BE SPREAD OVER PAGES.

VIEWS

BASE TABLE AS IT EXISTS VIEW AS THE PROGRAM’SSTORAGE LOGIC SEES IT.

TABLE S VIEW

S# SNAME STATUS CITY S# STATUS CITY

A VIEW CAN INCLUDE ALL OR SOME OF THE COLUMNS FROM ONE OR MORE BASE TABLES

VIEWS ARE CREATED FOR BASE TABLES OR VIEWS OR A COMBINATION OF VIEWS AND TABLES.

VIEWS ARE LOGICAL REPRESENTATION OF DATA THAT EXISTS IN BASE TABLES.

VIEWS ARE USED FOR SIMPLICITY AND SECURITY.

Views

A VIEW is a named table that is represented, not by its own physically separate, distinguishable stored data, but rather by its definition in terms of other named tables. VIEWS are created for base tables or views or a combination of views and tables.

When you define a view DB2 stores the definition of the view in the DB2 catalog. Data is physically present in base tables only and not in views. When a view is accessed then data is dynamically retrieved from the base table.

Advantages Of Views

1. They provide a certain amount of logical data independence in restructuring the database

2. They allow the same data to be seen by different users in different ways.

3. Automatic security is provided for data that is present in the base table by creating a view in which sensitive data is not visible.

INDEX SPACES

INDEX SPACE 1

INDEX 1

ONLY ONE INDEX IS STORED IN AN INDEX SPACE

INDEX SPACE IS AUTOMATICALLY CREATED WHEN THE CORRESPONDING INDEX IS CREATED.

PAGES IN AN INDEX SPACE ARE 4K BYTES IN SIZE.

INDEX SPACE FOR PARTITIONED TABLESPACE ARE PARTITIONED.

INDEX

INDEX 1

RID VALUE

PAGE P

T

INDEX CONSISTS OF TWO PARTS ,RECORD ID (RID) AND INDEXED VALUE.

A TABLE CAN HAVE ANY NUMBER OF ASSOCIATED INDEXES.

INDEXES ARE USED TO IMPROVE PERFORMANCE AND IN SOME CASES TO ENSURE UNIQUENESS.

IN THE EXAMPLE INDEX IS USED TO FIND A RECORD (T) IN PAGE P.

DB2 DETERMINES WHETHER TO USE AN INDEX OR NOT

Indexes

An index contains values from one or more of a table’s columns and a pointer to the record in a data which matches the index value. DB2 will find data more efficiently by scanning the index and following the pointer than by scanning the entire tablespace.

Record ID of index has two parts. First part is to identify the page where the record lies and the second part is the byte offset from the bottom of the page identifying the record. Index is structured in ascending or descending sequence on one or more columns. A given value of interest can be located quickly in the index because of their ascending or descending structure.

An index created on a table in a partitioned table space is a partitioned index and is divided into multiple index spaces.

Indexes are of two types, unique and non unique indexes. A non unique index can reference duplicate values, a UNIQUE INDEX will not. You can create an index any time after you create the table. But creating an index before loading the data provides significant performance advantages.

Indexes can be clustered or non clustered. A clustering index is one in which the records are physically stored in data pages in the sequential order of their index values. The index is used to control physical placement of the indexed records. Newly inserted records are physically stored such that the physical sequence of those records in storage closely approximates the logical sequence as defined by the index. In a non clustered index the records will not be in the order of index values.

A table can have any number of indexes but it can have only one clustered index.Clustering is extremely important for optimization purpose. The optimizer will try to choose an access path based on the clustering index .

For detailed explanation of indexes please refer ‘More about indexes’, chapter 12.

ALIASES

AN ALIAS IS AN ALTERNATIVE NAME FOR A TABLE OR VIEW. IT IS A QUALIFIED NAME THAT CAN BE USED BY ANY AUTHORIZATION ID.

AN ALIAS CAN BE DEFINED FOR A TABLE OR VIEW THAT WAS CREATED BY SOME OTHER USER AND FOR WHICH YOU WOULD OTHERWISE HAVE TO USE A FULLY QUALIFIED NAME

ALIASES WERE DESIGNED FOR A DISTRIBUTED ENVIRONMENT TO AVOID HAVING TO REFERENCE THE LOCATION QUALIFIER OF TABLE OR VIEW

ALIAS IS NOT PRIVATE TO THE CREATOR

AN ALIAS CAN BE DEFINED ON AN UNDEFINED NAME. THAT IS THE OBJECT ON WHICH THE ALIAS IS CREATED NEED NOT BE PRESENT AT THE CREATION TIME

Aliases

Aliases are useful for creating meaningful names for TABLES and VIEWS. ALIASES are created using CREATE ALIAS statement. One user can use an ALIAS created by another user since aliases are not private to the creator

EXAMPLE

Suppose user ALPHA creates a table called SAMPLE.

CREATE TABLE SAMPLE

The fully qualified name of the table SAMPLE is ALPHA.SAMPLE and another user BETA can refer to the table sample by its fully qualified name.

SELECT *FROM ALPHA.SAMPLE

The user BETA can create an alias called ZTEST for the table ALPHA.SAMPLE using create statement.

CREATE ALIAS ZTEST FOR ALPHA.SAMPLE

And now he can refer to the table SMPLE created by ALPHA by simply referring to the alias ZTEST

SELECT * FROM ZTEST

Another user GAMMA can also use BETA’S ALIAS ZTEST to refer to ALPHA’S SAMPLE table.

SELECT * FROM BETA.ZTEST

SYNONYMS

SYNONYMS ARE USEFUL FOR CREATING MORE MEANINGFUL NAME FOR A PERSON USING A TABLE OR VIEW

A SYNONYM IS AN UNQUALIFIED NAME THAT CAN ONLY BE USED BY THE AUTHORIZATION ID THAT CREATED IT.

A SYNONYM IS PRIVATE TO THE USER WHO CREATES IT

SYNONYM CANNOT REFER TO REMOTE TABLE IN A DISTRIBUTED DATA ENVIRONMENT

A SYNONYM CAN ONLY BE DEFINED ON THE NAME OF AN EXISTING TABLE OR VIEW.

Synonyms

A SYNONYM like an ALIAS is an alternative name for a table. Creating a SYNONYM for a table or view will allow the creator to refer to those tables and views by the more meaningful synonym created by him.

EXAMPLE

Suppose user ALPHA creates a table called SAMPLE.

CREATE TABLE SAMPLE

The fully qualified name of the table SAMPLE is ALPHA.SAMPLE and another user BETA can refer to the table sample by its fully qualified name.

SELECT * FROM ALPHA.SAMPLE

The user BETA can create a SYNONYM called ZTEST for the table ALPHA.SAMPLE using create statement.

CREATE SYNONYM ZTEST FOR ALPHA.SAMPLE

And now he can refer to the table SAMPLE created by ALPHA by simply referring to the SYNONYM ZTEST

SELECT * FROM ZTEST

However the user BETA and table ALPHA.SAMPLE must be at the same site. Also the name ZTEST is completely private to the user BETA. Another user GAMMA cannot use the synonym created by BETA and if it wants a synonym it should be created on ALPHA.SAMPLE.

DB2 CATALOG

DB2 CATALOG CONSISTS OF TABLES WHICH CONTAIN

INFORMATION ABOUT OBJECTS DEFINED UNDER THE

DB2 SYSTEM . WHEN A NEW TABLE IS CREATED

4 CATALOG TABLES ARE UPDATED . THEY ARE

SYSIBM.SYSTABLES , SYSIBM.SYSCOLUMNS .

SYSIBM.SYSTABLESPACE , SYSIBM.SYSTABAUTH

EXAMPLES OF CATALOG TABLES

SYSIBM.SYSTABLESCONTAINS INFORMATION OF A TABLE. WHEN A NEW TABLE IS CREATED DB2 INSERTS ONE ROW INTO THIS CATALOG TABLE.

SYSIBM.SYSCOLUMNSCONTAINS INFORMATION ABOUT THE COLUMNS IN A TABLE. THIS TABLE CONTAINS ONE ROW FOR EVERY COLUMN OF EACH ROW IN A TABLE .

SYSIBM.SYSTABLESPACE CONTAINS INFORMATION OF THE TABLE SPACE CREATED. THIS TABLE CONTAINS ONE ROW FOR EACH TABLESPACE.

SYSIBM.SYSTABAUTHCONTAINS INFORMATION OF THE TABLE NAMES AND AUTHORIZATION ID’s WHICH HAVE PRIVILEGES ON THAT TABLE

DB2 Catalog

The CATALOG in DB2 is a system database that contains information concerning various objects that are of interest to DB2 itself. Examples of such objects are tables, views, indexes, databases, plans, packages, access privileges, and so on. These information is essential, if the system is to able to do it’s job properly.

CATALOG itself contains TABLES and you can see the contents of catalog tables using normal query language ( SQL ). When you create, drop or alter any structure, DB2 updates or deletes rows of the catalog that describe the structure.

DBA ‘s and application programmers may use catalog tables to determine

Which application plan and packages use which indexes Which tablespaces, tables and indexes are in a database An index’s structure, whether unique or clustered or the number of levels

present in an index The amount of physical space used and remaining Who created an object and who owns it. Which plans and packages use objects in a database. Who has authorization to create objects Which plans and packages use which tables and tables and views Which synonyms and aliases have been created on tables and views Who is authorized to execute which plans and packages etc

Optimizer component of bind will use catalog information to choose best access strategy.

DB2 DIRECTORY

DB2 DIRECTORY CONTAINS INFORMATION

REQUIRED TO START DB2 AND DB2 USES

THE DIRECTORY DURING NORMAL OPERATION.

DB2 DIRECTORY CONSISTS OF A SET OF DB2

TABLES STORED IN 5 TABLE SPACES IN SYSTEM

DATABASE DSNDB01.

SKELETON CURSOR TABLESPACE (SCT02) CONTAINS PLANS

SKELETON PACKAGE TABLE (SPT01) CONTAINS PACKAGES

LOG RANGE TABLE SPACE (SYSLGRNX) CONTAINS THE RBA (RELATIVE BYTE ADDRESS ) THE LOG DATASET

SYSTEM UTILITIES TABLE SPACE (SYSUTILX) CONTAINS THE INFORMATION ABOUT RUNNING UTILITIES

THE DATABASE DESCRIPTOR TABLE SPACE (DBD01) CONTAINS INTERNAL CONTROL BLOCKS THAT DESCRIBE THE DATABASES EXISTING WITHIN DB2.

CANNOT ACCESS DIRECTORY USING SQL

ACTIVE AND ARCHIVE LOGS

DB2 RECORDS ALL DATA CHANGES AND SIGNIFICANTEVENTS IN A LOG AS THEY OCCUR

DB2 WRITES EACH LOG RECORD TO A DASD DATA SETCALLED THE ACTIVE LOG.

WHEN THE ACTIVE LOG IS FULL, DB2 COPIES THE CONTENTSOF THE ACTIVE LOG TO A DASD CALLED THE ARCHIVE LOG

IN THE CASE OF FAILURE DB2 USES LOGS TO RECOVER DATA.

THE ARCHIVE LOG CAN CONSIST OF UP TO 1000 DATA SETS EACH OF WHICH IS A SEQUENTIAL DATA SET.

BUFFER POOLS

BUFFER POOLS ARE AREAS OF VIRTUAL

STORAGE THAT TEMPORARILY STORE PAGES

OF TABLE SPACES OR INDEXES.

THE DATA REMAINS IN THE BUFFER UNTIL

DB2 DECIDES TO USE THE SPACE FOR

ANOTHER PAGE

BUFFER POOLS HOLD THE MOST FREQUENTLY ACCESSED DATA.

USING BUFFER POOLS IMPROVE PERFORMANCE.

DB2 ALLOWS TO USE 50 BUFFER POOLS THAT CONTAIN 4KB BUFFERS AND 10 BUFFER POOLS THAT CONTAIN 32KB BUFFERS.

4KB BUFFER POOLS ARE BP0 TO BP49

32KB BUFFER POOLS ARE BP32K TO BP32K9

Buffer Pools

Buffer pools, also known as virtual buffer pools, are areas of virtual storage used temporarily to store pages of table spaces or indexes. When an application program needs to access a row of a table, DB2 retrieves the page containing that row and places the page in a buffer. If the row is changed, the buffer must be written back to the table space. If the needed data is already in a buffer, the application program will not have to wait for it to be retrieved from DASD. The result is faster performance.

DB2 can provide 2 types of buffer pools, 4K and 32K buffer pools. There are fifty 4K buffer pools named BP0, BP1, P49 and ten 32K buffer pools named BP32K, BP32K1, BP32K9. DB2 manages each buffer pools separately . Generally system administrator decides how much memory to allocate for buffer pools. The more memory allocated to buffer pool the more data it can hold and therefore the greater the likelihood that an application request will find the data there.

4. Data TypesThis chapter describes various data types used in DB2 and their examples. COBOL declarations of the corresponding DATA TYPES are also included.

The sub divisions of this chapter are

4.1. Numeric Data

4.1.1. Nulls

4.2. String Data

4.3. Character Format

4.4. Date/Time Data

4.5. Equivalent Cobol Declarations Of Data Types

DATA TYPES

EVERY COLUMN IN A TABLE IS ASSIGNED A SPECIFIC TYPE AND SIZE OF DATA

CATEGORIES OF DATA TYPES

NUMERIC DATASTRING DATADATE / TIME DATA

EACH COLUMN IN A TABLE MUST BE DEFINED

COLUMN DEFINITION MUST INCLUDE THE DATA TYPE AND SIZE

ALL DATA TYPES CAN INCLUDE NULL VALUES.

NUMERIC DATA

SMALLINT : TWO BYTE BINARY INTEGER , 15 BITS AND SIGN.

INTEGER : FOUR BYTE BINARY INTEGER, 31 BITS AND SIGN.

DECIMAL (P,Q): PACKED DECIMAL NUMBER HAVING P DIGITS OF WHICH Q DIGITS ARE AFTER THE ASSUMED DECIMALPOINT

FLOAT (M) IF M IS BETWEEN 1 AND 21 THEN IT IS SINGLE REAL PRECISION FLOATING POINT AND IT OCCUPIES FOUR

BYTES. IT CAN ALSO BE REFERRED AS REAL

FLOAT (M) IF M IS BETWEEN 22 AND 53 THEN IT IS SINGLEFLOAT PRECISION FLOATING POINT AND IT OCCUPIES EIGHT

BYTES. IT CAN ALSO BE REFERRED AS FLOAT

RANGE OF VALUES

SMALLINT -32768 to +32767

INTEGER -2147483648 to +2147483647

DECIMAL (P ,Q) MAXIMUM 31 DIGITS0 < P < 32 AND ( 0 <= Q <= P )

REAL 5.4E-79 to 7.2E+75.FLOAT 5.4E-79 to 7.2E+75.

EXAMPLES OF NUMERIC DATA DECLARATION

SPKZ DECIMAL(5, 2) DRU SMALLINTHDNR INTEGER

NULLS

SQL SYSTEMS LIKE DB2 REPRESENT MISSING INFORMATION IN A COLUMN BY MEANS OF SPECIAL MARKERS CALLED NULLS.

THE PRESENCE OF NULL VALUE IN A COLUMN DEPENDS ON THE COLUMN DEFINITION .

THREE OPTIONS, SPECIFIED IN COLUMN DEFINITION WHICH DEAL WITH NULL VALUES ARE

NOT NULL NULL NOT NULL WITH DEFAULT

IF A COLUMN IS DECLARED AS NOT NULL THEN DB2 WILL NOT ALLOW NULL VALUES ON THAT COLUMN

WHEN A COLUMN IS DECLARED AS NULL WHICH IS THE DEFAULT, DB2 WILL ALLOW NULL VALUE ON THAT COLUMN

NOT NULL WITH DEFAULT MEANS THAT THE COLUMN IN QUESTION CANNOT CONTAIN NULLS, BUT IT IS STILL LEGAL TO OMIT A VALUE FOR THE COLUMN

EXAMPLES

SPKZ DECIMAL(5, 2) NULLDRU SMALLINT NOT NULLHDNR INTEGER NOT NULL WITH DEFAULT

Nulls

Null values are used in a table when actual values are unknown. Suppose the weight of a part in the SUPPLIER-PARTS DATABASE is null, then it means that

(1) The part exists(2) It does have a weight (3) We do not know what the value is

In other words we do not know a genuine weight value that can sensibly be put in the weight slot in the row for the part in question. Instead we mark that slot as null and we interpret that mark to mean precisely that we do not know what the real value is. we can insert a null value in the WEIGHT column if it is declared as NULL. But if it is declared as NOT NULL WITH DEFAULT, it is possible to insert a row into the table without specifying a value for WEIGHT column. In that case the column will contain default values corresponding to the column data type.

Suppose that NOT NULL is specified for column WEIGHT in the SUPPLIER-PARTS DATABASE, then this will guarantee that every row in table P will always contain a genuine (not null) WEIGHT value. In other words a value must always be provided for column WEIGHT when a row is inserted into the P table.

If a given column is allowed to contain nulls and a row inserted into the table with no value provided for that column DB2 will automatically place a null in that position. Suppose that the WEIGHT column in supplier-table database is specified as NULL, then we can insert a row in the table P without specifying a value for WEIGHT. DB2 will automatically put a null value in that column.

NOT NULL WITH DEFAULT means the column in question cannot contain nulls but it is nevertheless still legal to omit a value for the column on insert. If a row is inserted and no value is provided for some column to which NOT NULL WITH DEFAULT applies DB2 automatically places one of the following non null default values in that position.

Zero for numeric items Blanks for fixed length string columns Empty (zero length string) for varying length string columns The value of CURRENT DATE or CURRENT TIME or CURRENT TIMESTAMP

for variables declared with attributes DATE, TIME or TIMESTAMP.

STRING DATA

CHARACTER FORMAT

CHARACTER(n) : FIXED LENGTH STRING OF n 8 BIT CHARACTERSOCCUPYING N BYTES

VARCHAR(n) : VARYING LENGTH STRING UP TO n 8 BIT CHARACTERSOCCUPYING n+2 BYTES . FIRST TWO BYTES ARE USED FOR STORING THE LENGTH OF THE VARIABLE

LONG VARCHAR : VARYING LENGTH CHARACTER STRING WHOSEMAXIMUM LENGTH WILL BE DECIDED BY DB2

RANGE OF VALUES

CHARACTER(n) : 1 TO 254

VARCHAR(n) : MUST BE LESS THAN PAGE SIZE (4K)

LONG VARCHAR : MAXIMUM LENGTH IS DETERMINED BYTHE AMOUNT OF SPACE AVAILABLE INA PAGE

EXAMPLES OF CHARACTER DATA REPRESENTATION

SPKZ CHAR (20)NUM VARCHAR (60)VAR LONG VARCHAR

GRAPHIC FORMAT

GRAPHIC(n) : FIXED LENGTH STRING OF N 16 BIT CHARACTERSOCCUPYING 2n BYTES

VARGRAPHIC(n) : VARYING LENGTH STRING UP TO N 16 BIT CHARACTERS OCCUPYING 2n+2 BYTES . FIRST TWO BYTES ARE USED FOR STORING THE LENGTH OF THE VARIABLE

LONG VARGRAPHIC : VARYING LENGTH 16 BIT CHARACTER STRING WHOSE MAXIMUM SIZE WILL BE DECIDED BY DB2

RANGE OF VALUES

GRAPHIC(N) : 1 TO 127

VARGRAPHIC(N) : N MUST BE LESS THAN HALF THE PAGE SIZE (2K)

LONG VARGRAPHIC: MAXIMUM LENGTH IS DETERMINED BY THEAMOUNT OF SPACE AVAILABLE IN A PAGE

EXAMPLES OF GRAPHIC DATA DECLARATIONS

TABKOST GRAPHIC (10)TABIDVARGRAPHIC (80)TEMP LONG VARRRAPHIC

DATE / TIME DATA

INTERNAL REPRESENTATIONS

DATE YYYYMMDD

TIME HHMMSS

TIMESTAMP YYYYMMDDHHMMSSNNNNNN

DATE IS REPRESENTED AS A SEQUENCE OF EIGHT UNSIGNED PACKED DECIMAL DIGITS OCCUPYING 4 BYTES

TIME IS REPRESENTED AS A SEQUENCE OF SIX UNSIGNED PACKED DECIMAL DIGITS OCCUPYING 3 BYTES

TIMESTAMP IS REPRESENTED AS A SEQUENCE OF 20 UNSIGNED PACKED DECIMAL DIGITS OCCUPYING 10 BYTES

EXAMPLES OF DATE TIME DECLARATIONS

CCTEMP DATECCDAT TIMECCSTAMP TIMESTAMP

Date / Time Data

Columns whose data types are DATE, TIME, OR TIMESTAMP are represented in an internal form that is transparent to the user of SQL. But DATES, TIMES, AND TIMESTAMPS can also be represented by DATE/TIME strings. These are character string representations of date values. When you retrieve date/time values they must be assigned to properly declared character string variables.

When a date or time is assigned to a variable, the string format is determined by a precompiler option or subsystem parameter. When a string representation of a datetime value is used in other operations, it is converted to a datetime value. However, this can be done only if the string representation is compatible with the date / time value

Example

The ISO date format ‘1987-10-12’ is internally stored in 4 bytes. But you must assign a variable with 10 bytes as host variable for retrieving the above date.

EQUIVALENT COBOL DECLARATIONS OF DATA TYPES

DATATYPE COBOL DECLARATION

CCTEMP SMALLINT 01 CCTEMP PIC S9(4) COMP. CCTEMP INT 01 CCTEMP PIC S9(9) COMP.

CCTEMP DECIMAL(9,3) 01 CCTEMP PIC S9(6)V9(3) COMP-3.

CCTEMP FLOAT(21) 01 CCTEMP COMP-1.

CCTEMP FLOAT(53) 01 CCTEMP COMP-2.

CCTEMP CHAR(10) 01 CCTEMP PIC X(10).

CCTEMP VARCHAR(80) 01 CCTEMP 49 VARLEN PIC S9(4) COMP. 49 CCVAR PIC X(80).

5. SQL Programming

IN DB2 operations are done using structured query language. This chapter explains types of SQL and their usage. SQL statements are divided into

DDL Statements DML Statements Control Statements

SQL PROGRAMMING

SQL (STRUCTURED QUERY LANGUAGE ) IS THE LANGUAGE USED TO ACCESS DATAIN DB2 TABLES

SQL

DDL DML CONTROL STATEMENTS

DDL (DATA DEFINITION LANGUAGE)

CREATE ALTER DROP

DML (DATA MANIPULATION LANGUAGE)

SELECT UPDATE INSERT DELETE

CONTROL STATEMENTS

GRANT REVOKE COMMIT ROLLBACK

5.1. DDL Statements

Data definition language statements used for creating, changing and dropping DB2 objects. The following sections explain these statements with suitable examples

5.1.1. Create Database

5.1.2. Create Table Space

5.1.3. Create Table

5.1.3.1. Keys

5.1.3.2. Primary Keys

5.1.3.3. Foreign Keys

5.1.4. Create View

5.1.5. Create Index

5.1.6. Alter Table

5.1.7. Drop

CREATE DATABASE

THE CREATE DATABASE STATEMENT DEFINES ADB2 DATABASE TO THE DB2 SUBSYSTEM. THE NAME MUST NOT START WITH DSNDB AND MUST NOT IDENTIFY AN EXISTING DATABASE

IN THIS STATEMENT YOU CAN SPECIFY THE NAME OF BUFFERPOOL AND STORAGE GROUP FOR TABLE SPACES AND INDEXES WITHIN THE DATABASE

IF BUFFER POOL IS NOT SPECIFIED IN THE CREATE DATABASE STATEMENT THEN DEFAULT BUFFER POOL USED IS BP0.

IF STORAGE GROUP IS NOT SPECIFIED IN THE CREATE DATABASE STATEMENT THEN DEFAULT STORAGE GROUP USED IS SYSDEFLT.

EXAMPLE

CREATE DATABASE "D2110K"BUFFERPOOL BP2STOGROUP "SGDB2O";

CREATE TABLESPACE

THE CREATE TABLESPACE STATEMENT ALLOCATES SPACE FOR TABLES. THIS STATEMENT CREATES A SIMPLE, SEGMENTED, OR PARTITIONED TABLE SPACE IN THE SPECIFIED DATABASE.IF DATABASE IS NOT SPECIFIED THEN TABLESPACE IS CREATED IN THE DEFAULT DATABASE DSNDB04

EXAMPLES

1. CREATE TABLESPACE "S110K10" IN "D2110K"USING STOGROUP "SGDB2O"PRIQTY 100 SECQTY 52 FREEPAGE 0 PCTFREE 5BUFFERPOOL BP0LOCKSIZE ANYCLOSE NO SEGSIZE 8;

2. CREATE TABLESPACE "S110L40" IN "D2110L"USING STOGROUP "SGDB2O"PRIQTY 100 SECQTY 52 ERASE NONUMPARTS 16FREEPAGE 0 PCTFREE 5BUFFERPOOL BP2LOCKSIZE PAGECLOSE NO;

Create Table Space

Many parameters can be specified in the CREATE TABLESPACE statement which decides the type of tablespace, the SIZE of VSAM datasets which hold the tables and indexes, the amount and distribution of space left free in the datasets, the amount of data covered by concurrency control locks etc. All of these decisions made during table space creation hold performance implications. If the developer does not specify choices for any of these parameters DB2 will use default values.

In the given examples DB2 automatically creates VSAM linear datasets needed for the tablespace within the specified storage group. Each data set will be defined on a volume of the storage group specified in the create tableapace statement. The values specified for PRIQTY and SECQTY determine the primary and secondary allocations for the data set.

Erase parameter Indicates whether the DB2-managed data sets for the tablespace are to be erased when they are deleted during the execution of a utility or an SQL statement that drops the table space. ERASE NO does not erase the data sets. ERASE YES erases the data sets. As a security measure, DB2 overwrites all data in the data sets with zeros before they are deleted.

FREEPAGE parameter Specifies how often to leave a page of free space when the table space or partition is loaded or reorganized. The default is FREEPAGE 0, leaving no free pages. PCTFREE parameter indicates what percentage of each page to leave as free space when the table is loaded or reorganized. The default is PCTFREE 5.

LOCKSIZE parameter Specifies the size of locks used within the table space . For more information please refer chapter 9.

NUMPARTS parameter Indicates that the table space will be partitioned and the number of partitions in that tablespace.

BUFFERPOOL parameter Identifies the buffer pool to be used for the table space and determines the page size of the table space.

CLOSE parameter specifies whether or not the data sets are eligible to be closed when the table space is not being used or the limit on the number of open data sets is reached. CLOSE YES says the dataset is eligible for closing. This is the default. CLOSE NO specifies that the dataset is not eligible for closing.

SEGSIZE parameter Indicates that the table space will be segmented and specifies, how many pages are to be assigned to each segment. If SEGSIZE and NUMPARTS parameters are not given, then the table space will be SIMPLE

CREATE TABLE

CREATE TABLE STATEMENT CREATES A TABLE IN ATABLESPACE. TABLE NAME IS UNIQUE FOR A USER.

IF USERA CREATES TABLEA THEN FULLY QUALIFIED

NAME WILL BE USERA.TABLEA. USERA CAN SIMPLY USE

THE NAME TABLEA BUT OTHER USERS MUST SPECIFY FULLY QUALIFIED NAME

EXAMPLES

1. CREATE TABLE D2110L.SP(,S# CHAR(5) NOT NULL,P# CHAR(6) NOT NULL,QTY INTEGER NOT NULL,PRIMARY KEY( S# , P# ),FOREIGN KEY ( S# ) REFERENCES S,,FOREIGN KEY ( P# ) REFERENCES P)IN D2110L.TABSP

(2) CREATE TABLE D2110L.SP LIKE D2110K.TAB IN D2110L.TABSP;

KEYS

A KEY IS ONE OR MORE COLUMNS THAT ARE IDENTIFIED AS SUCH IN THE DESCRIPTION OF A TABLE, AN INDEX, OR A REFERENTIAL CONSTRAINT.


S1 SMITH 20 LONDON S2 JONES 10 PARIS S3 BLAKE 30 PARIS

KEY

A KEY IDENTIFIES A ROW OF DATA

A ROW IN ONE TABLE CAN CARRY THE KEY OF ANOTHER TABLE SO KEYS ARE USED FOR RELATING TABLES

A KEY COMPOSED OF MORE THAN ONE COLUMN IS CALLED A COMPOSITE KEY. A COMPOSITE KEY IS AN ORDERED SET OF COLUMNS OF THE SAME TABLE.

A UNIQUE KEY IS A KEY THAT IS CONSTRAINED SO THAT NO TWO OF ITS VALUES ARE EQUAL.

PRIMARY KEY

A PRIMARY KEY IS A UNIQUE KEY THAT IS A PART OF THE DEFINITION OF A TABLE


P1 NUT RED 12 LONDON P2 BOLT GREEN 17 PARIS P3 SCREW BLUE 17 ROME P4 SCREW RED 14 LONDON P5 CAM BLUE 12 PARIS P6 COG RED 19 LONDON

PRIMARY KEY

PRIMARY KEY OF A TABLE IS THE UNIQUE IDENTIFIER FOR THAT TABLE

PRIMARY KEY CAN BE COMPOSITE

A TABLE CANNOT HAVE MORE THAN ONE PRIMARY KEY, AND THE COLUMNS OF A PRIMARY KEY CANNOT CONTAIN NULL VALUES.

WHEN A PRIMARY KEY IS DEFINED ON A TABLE, A UNIQUE INDEX MUST BE CREATED ON THAT PRIMARY KEY

FOREIGN KEYS

A FOREIGN KEY IS A COLUMN OR COMBINATION OF COLUMNS IN ONE TABLE WHOSE VALUES ARE REQUIRED TO MATCH VALUES OF THE PRIMARY KEY IN SOME OTHER TABLE.

TABLE S TABLE SP


S1 SMITH 20 LONDON S1 P1 300 S2 JONES 10 PARIS S1 P2 200

S2 P1 300 ….. ……… … …… …. …. …..

PRIMARY KEY IN S FOREIGN KEY IN SP

A FOREIGN KEY VALUE REPRESENTS A REFERENCE TO THE ROW CONTAINING THE MATCHING PRIMARY KEY VALUE.

THE TABLE THAT CONTAINS THE FOREIGN KEY IS KNOWN AS THE DEPENDENT TABLE AND THE TABLE THAT CONTAINS THE PRIMARY KEY IS KNOWN AS THE PARENT TABLE.

EACH VALUE OF A FOREIGN KEY MUST BE WHOLLY NULL OR WHOLLY NON NULL. THAT IS IF FOREIGN KEY IS A COMPOSITE KEY THEN ALL COMPONENTS OF THAT KEY MUST BE NULL OR NON NULL, NOT A MIXTURE.

CREATE VIEW

THE CREATE VIEW STATEMENT CREATES A VIEW ON TABLES OR VIEWS. IF THE VIEW NAME IS UNQUALIFIED THEN THE AUTHORIZATION ID IS THE IMPLICIT QUALIFIER

BASE TABLE: S


VIEW : GOOD_SUPPLIERS

S# STATUS CITY

IF YOU DO NOT SPECIFY A LIST OF COLUMN NAMES, THE COLUMNS OF THE VIEW INHERIT THE NAMES OF THE COLUMNS OF THE RESULT TABLE OF THE SUB SELECT.

EXAMPLE

CREATE VIEW GOOD_SUPPLIERSAS SELECT S# , STATUS, CITYFROM SWHERE STATUS > 15 ;

CREATE INDEX

THE CREATE INDEX STATEMENT CREATES A PARTITIONEDOR NON PARTITIONED INDEX AND AN INDEX SPACE.INDEX CAN BE CREATED ON ONE OR MORE COLUMNS.WHEN YOU CREATE UNIQUE INDEX THE KEY CANNOT HAVEDUPLICATE VALUES. UNIQUE INDEX SHOULD BE CREATED FOR A PRIMARY KEY.

EXAMPLES

1. CREATE UNIQUE INDEX D2110K.I11010U1ON D2110K.S(S#)BUFFERPOOL BP0USING STOGROUP SGDB2OPRIQTY 40SECQTY 20CLOSE NO;

2. CREATE INDEX D2110P.I11010U2ON D2110N.P (P# DESC)

3. CREATE UNIQUE INDEX D2110L.I11010U3ON D2110L.SP (S#, P#)

ALTER TABLE

THE ALTER TABLE STATEMENT CHANGES THE DESCRIPTION OF A TABLE

TO ADD MULTIPLE COLUMNS ,CODE MULTIPLE ALTERSTATEMENTS.

ADDED COLUMNS MUST ACCEPT NULL OR NOT NULLWITH DEFAULT VALUES

THIS COMMAND CANNOT BE USED FOR DELETING A COLUMN

PRIMARY AND FOREIGN KEYS CAN BE CREATED AND DROPPED USING THIS COMMAND

EXAMPLES

1. ALTER TABLE D2110.PADD PRICE SMALLINT;

2. ALTER TABLE D2110K.SPFOREIGN KEY(P#) REFERENCES D2110K.PON DELETE CASCADE;

3 ALTER TABLE D2110K.PPRIMARY KEY(P#);

4 ALTER TABLE D2110K.SDROP PRIMARY KEY(S#);

DROP

THE DROP STATEMENT DELETES AN OBJECT

ALIAS alias nameDATABASE database nameINDEX index nameSTOGROUP stogroup name

DROP SYNONYM synonym nameTABLE table name TABLESPACE table space nameVIEW view namePACKAGE collection-id.package-id

FREE PLAN

WHEN AN OBJECT IS DROPPED ALL OBJECTS THAT ARE DIRECTLY OR INDIRECTLY DEPENDENT ON THAT OBJECT ARE DELETED

THE OBJECT’S DESCRIPTION IS DELETED FROM THE CATALOG TABLE.

Drop

The results of dropping various objects are given below.

1. Dropping an alias has no effect on any view or synonym that was defined using the alias.

2. When you drop the database , the database and all of its table spaces, tables, index spaces, and indexes are dropped.

3. Whenever an index is directly or indirectly dropped ,it’s index space is also dropped.

4. When the synonym is dropped, view or alias that defined using the synonym are not dropped.

5. Whenever a table is directly or indirectly dropped, all privileges on the table, all referential constraints in which the table is a parent or dependent, and all synonyms, views, and indexes defined on the table are also dropped.

6. Whenever a table space is directly or indirectly dropped, all tables in the table space are also dropped.

7. Whenever a view is directly or indirectly dropped, all privileges on the view and all synonyms and views that are defined on the view are also dropped.

8. when the package version is dropped, all privileges on the package are dropped and all plans that are dependent on the execute privilege of the package are invalidated.

5.2. DML Statements

Data manipulation statements are used for retrieving data from DB2 tables. The following statements together known as data manipulation language.

5.2.1. Select

5.2.1.1. Comparison Operators

5.2.1.2. Select Distinct

5.2.1.3. Multiple Conditions

5.2.1.4. Order By

5.2.1.5. In, Between

5.2.1.6. Partial Search

5.2.1.7. Aggregate Functions

5.2.1.8. Group By

5.2.1.9. Having

5.2.2. Joining Tables

5.2.3. Sub Queries

5.2.4. Union

5.2.5. Insert

5.2.6. Update

5.2.7. Delete

DML STATEMENTS

SELECT

SQL SELECT

REQUIRED SEQUENCE

SELECT

FROM

WHERE

ORDER BY

EXAMPLE

Q: GET SUPPLIER NUMBERS AND STATUS FORSUPPLIERS IN PARIS, IN DESCENDING ORDER OF STATUS

QUERYSELECT S# , STATUS

-TELLS WHICH COLUMNS TO USE

FROM S-TELLS WHICH TABLES TO USE

WHERE CITY = ‘PARIS’-TELLS WHICH ROWS TO USE

ORDER BY STATUS DESC ;-TELLS HOW TO SEQUENCE THE RESULT

RESULT

S# STATUS

S3 30S2 10

COMPARISON OPERATORS

= EQUAL

^= NOT EQUAL

<> NOT EQUAL

> GREATER THAN

^> NOT GREATER THAN >= GREATER THAN OR EQUAL

< LESS THAN

^< NOT LESS THAN

<= LESS THAN OR EQUAL

SELECT DISTINCT

SELECT DISTINCT IS TO ELIMINATE DUPLICATE ROWS

Q : GET PART NUMBERS FOR ALL PARTS SUPPLIED WITH REDUNDANT DUPLICATES ELIMINATED

QUERY : SELECT DISTINCT P#FROM SP;

RESULT

P#

P1P2P3 P4P5P6

MULTIPLE CONDITIONS

MULTIPLE CONDITION RETRIEVAL

AND OR

Q1 : GET SUPPLIER NUMBERS AND SUPPLIER NAMES OF SUPPLIERS LOCATED INLONDON AND HAVING STATUS CODE 20

Q2 : GET SUPPLIER NUMBERS AND SUPPLIERNAMES OF SUPPLIERS WHOSE STATUS IS 10OR 20.

QUERY 1 : SELECT S#, SNAMEFROM SWHERE STATUS = 20AND CITY = ‘LONDON’ ;

QUERY 2 : SELECT S#, SNAMEFROM SWHERE STATUS = 10 OR STATUS = 20 ;

RESULT 1 RESULT 2

S# SNAME S# SNAME

S1 SMITH S1 SMITH S4 CLARK S2 JONES

S4 CLARK

ORDER BY

SPECIFY COLUMN NAME AND TELL WHETHERASCENDING OR DESCENDING SEQUENCE

THE DEFAULT SEQUENCE IS ASCENDING

QUERY: SELECT P# , ‘ WEIGHT IN GRAMS = ’ , WEIGHT * 454FROM PORDER BY 3, P# ;

RESULT

P#

P1 WEIGHT IN GRAMS = 5448P5 WEIGHT IN GRAMS = 5448P4 WEIGHT IN GRAMS = 6356P2 WEIGHT IN GRAMS = 7718P3 WEIGHT IN GRAMS = 7718P6 WEIGHT IN GRAMS = 8448

IN, BETWEEN

IN : TO MATCH ONE OF A LIST OF VALUES

BETWEEN: TO SELECT A RANGE OF VALUES

CAN USE NOT IN AND NOT BETWEEN

Q1 : GET PART NUMBERS , PNAME AND WEIGHT OFPARTS WHOSE WEIGHT IS ANY ONE OF THE FOLLOWING: 12 ,16 ,17

Q2 : GET PART NUMBERS , PNAME AND WEIGHT OFPARTS WHOSE WEIGHT IS IN THE RANGE 16 TO19 INCLUSIVE

QUERY 1 SELECT P# , PNAME , WEIGHTFROM PWHERE WEIGHT IN ( 12 , 16 , 17 ) ;

QUERY 2 SELECT P# , PNAME , WEIGHTFROM PWHERE WEIGHT BETWEEN 16 AND 19 ;

RESULT 1 RESULT 2

P# PNAME WEIGHT P# PNAME WEIGHT

P1 NUT 12 P2 BOLT 17 P2 BOLT 17 P3 SCREW 17 P3 SCREW 17 P6 COG 19 P5 CAM 12

PARTIAL SEARCH

TO SEARCH ON A SUBSET OF CHARACTERS : LIKE

NOT TO SEARCH ON A SUBSET OF CHARACTERS : NOT LIKE

QUERY 1 : SELECT S# , SNAME , CITYFROM S WHERE CITY LIKE ‘L%’ ;

QUERY 2 : SELECT S# , SNAME , CITYFROM S WHERE SNAME LIKE ‘%S’ ;

QUERY 3 : SELECT S# , SNAME , CITYFROM S WHERE CITY NOT LIKE ‘%A%’ ;

QUERY 4 : SELECT S# , SNAME , CITYFROM S WHERE CITY LIKE ‘%DON’ ;

QUERY 5 : SELECT S# , SNAME , CITYFROM S WHERE SNAME LIKE ‘_L%’ ;

RESULT 1

S# SNAME CITY

S1 SMITH LONDON S4 CLARK LONDON

RESULT 2

S# SNAME CITY

S2 JONES PARIS S5 ADAMS ATHENS

RESULT 3

S# SNAME CITY


RESULT 4

S# SNAME CITY


RESULT 5

S# SNAME CITY S3 BLAKE PARIS S4 CLARK LONDON

AGGREGATE FUNCTIONS

COUNT : NUMBER OF VALUES IN THE COLUMN

SUM : SUM OF VALUES IN THE COLUMN

AVG : AVERAGE OF VALUES IN THE COLUMN

MAX : MAXIMUM OF VALUES IN THE COLUMN

MIN : MINIMUM OF VALUES IN THE COLUMN

Q1 : GET THE TOTAL NUMBER OF SUPPLIERS.

Q2 : GET THE TOTAL QUANTITY, AVERAGE QUANTITY,MAXIMUM QUANTITY AND MINIMUM QUANTITY OFPART P2 SUPPLIED

QUERY 1 : SELECT COUNT(*)FROM S;

QUERY 2 : SELECT SUM (QTY) , AVG (QTY) , MAX (QTY) , MIN (QTY)FROM SPWHERE P# = ‘P2’ ;

RESULT 1 RESULT 2

5 1000 250 400 200

GROUP BY

WITH GROUP BY, A COLUMN FUNCTION RESULTS IN A SINGLE VALUE FOR EACH GROUP

Q : FOR EACH PART SUPPLIED GET THE PART NUMBER AND THE TOTAL SHIPMENT QUANTITYFOR THAT PART

QUERY : SELECT P# , SUM (QTY)FROM SPGROUP BY P# ;

RESULT

P# P1 600 P2 1000 P3 400 P4 500 P5 500 P6 100

HAVING

HAVING IS USED TO GET SOME SPECIFIC ROWS, FROM THE ROWSOBTAINED BY GROUP BY CLAUSE, WHICH SATISFY THE CONDITIONGIVEN IN THE HAVING CLAUSE.

HAVING IS USED TO ELIMINATE GROUPS JUST AS WHERE IS USED TO ELIMINATE ROWS.

Q: GET PART NUMBERS FOR ALL PARTS SUPPLIED BY MORE THAN ONE SUPPLIER

QUERY : SELECT P#FROM SPGROUP BY P#HAVING COUNT (*) > 1.

RESULT P# P1 P2 P4 P5

JOINING TABLES

IT IS A QUERY IN WHICH DATA IS RETRIEVED FROM MORE THAN ONE TABLE

Q: GET ALL COMBINATIONS OF SUPPLIER AND PART INFORMATION SUCH THAT THE SUPPLIER CITYFOLLOWS THE PART CITY IN ALPHABETICAL ORDER

QUERY : SELECT S.* , P.*FROM S , PWHERE S.CITY > P.CITY

RESULT

S# SNAME STATUS S.CITY P# PNAME COLOR WEIGHT P.CITY

S2 JONES 10 PARIS P1 NUT RED 12 LONDON S2 JONES 10 PARIS P4 SCREW RED 14 LONDON S2 JONES 10 PARIS P6 COG RED 19 LONDON S3 BLAKE 30 PARIS P1 NUT RED 12 LONDON S3 BLAKE 30 PARIS P4 SCREW RED 14 LONDON S3 BLAKE 30 PARIS P6 COG RED 19 LONDON

SUB QUERIES

A SUB QUERY IS A SELECT-FROM-WHERE EXPRESSIONTHAT IS NESTED INSIDE ANOTHER SUCH EXPRESSION

MAXIMUM 15 LEVELS ARE POSSIBLE IN A NESTED SUB SELECT

Q: GET SUPPLIER NAMES FOR SUPPLIERS WHO SUPPLY

PART P2.

QUERY : SELECT SNAMEFROM SWHERE S# IN ( SELECT S#FROM SPWHERE P# = ‘P2’ ) ;

RESULT

SNAME

SMITHJONESBLAKECLARK

UNION

THE RESULTS OF ONE OR MORE RELATIONS ARE MIXED TO FORM A SINGLE RELATION USING UNION .

Q: GET PART NUMBERS FOR PARTS THAT EITHERWEIGH MORE THAN 16 POUNDS OR ARESUPPLIED BY SUPPLIER S2

QUERY : SELECT P#FROM PWHERE WEIGHT > 16UNIONSELECT P#FROM SP WHERE S# = ‘S2’ ;

RESULT

P1P2P3P6

INSERT

THE INSERT STATEMENT INSERTS A NEW ROW INTO THE TABLE. YOU CAN EITHER INSERT VALUES FORALL COLUMNS OR OMIT VALUES. BUT OMITTING AA VALUE FOR SOME COLUMN DEPENDS ON THEWAY THE COLUMN WAS DEFINED

Q1 : ADD PART P8 (A SPROCKET , COLOR PINK , WEIGHT 14 , CITY NICE ) TO TABLE P

Q2 : ADD PART P7 (CITY ATHENS , WEIGHT 24 ) NAMEAND COLOR AT PRESENT UNKNOWN. ASSUME THAT THE COLUMNS PNAME AND COLOR ARE CREATED WITH NULL ATTRIBUTE SPECIFICATION.

QUERY 1 : INSERT INTO PVALUES ( ‘P8’, ‘SPROCKET’, ‘PINK’, 14, ‘NICE’ ) ;

QUERY 2 : INSERT INTO P ( P#, CITY, WEIGHT )VALUES ( ‘P7’, ‘ATHENS’, 24 );


… …. … .... ……. P8 SPROCKET PINK 14 NICE RESULT 1 P7 ? ? 24 ATHENS RESULT 2

UPDATE

THE UPDATE STATEMENT UPDATES THE VALUES OF SPECIFIED COLUMNS IN ROWS OF A TABLE ORVIEW. UPDATING A ROW OF A VIEW UPDATES AROW OF THE TABLE ON WHICH THE VIEW IS BASED.

Q : CHANGE THE COLOR OF PART P1 TO YELLOW ,INCREASE IT’S WEIGHT BY 5 , AND SET IT’S CITYTO UNKNOWN. ASSUME THAT THE DEFINITIONOF P.CITY ALLOWS NULL VALUES.

QUERY : UPDATE PSET COLOR = ‘YELLOW’ ,WEIGHT = WEIGHT + 5CITY = NULL WHERE P# = ‘P1’ ;

RESULT

P# PNAME COLOR WEIGHT CITY … … … … … P1 NUT YELLOW 17 ? … … … … …

DELETE

THE DELETE STATEMENT DELETES ROWS FROMA TABLE OR VIEW. DELETING A ROW FROM AVIEW DELETES THE ROW FROM THE TABLE ONWHICH THE VIEW IS BASED.

SINGLE ROW DELETE

Q1: DELETE SUPPLIER S5

MULTIPLE ROW DELETE

Q2 : DELETE ALL SHIPMENTS WITH QUANTITY GREATER THAN 300

QUERY 1 : DELETEFROM SWHERE S# = ‘S5’ ;

QUERY 2 : DELETEFROM SPWHERE QTY > 300 ;

5.3. Control Statements

Statements other than DDL and DML are explained in this section. They are

5.3.1. Grant

5.3.2. Revoke

5.3.3. Commit

5.3.4. Roll Back

CONTROL STATEMENTS

GRANT

TO PERFORM ANY OPERATION ON ANY OBJECT THEUSER MUST HOLD THE APPROPRIATE PRIVILEGE FOR THE OPERATION AND THE OBJECT IN QUESTION .THE GRANT STATEMENT GRANTS PRIVILEGES ON ANOBJECT TO AUTHORIZATION IDS.

TABLE PRIVILEGES

GRANT SELECT ON TABLE S TO CHARLY ;

GRANT SELECT , UPDATE (STATUS , CITY ) ON TABLE S TO JUDY, JACK, JOHN ;

GRANT ALL PRIVILEGES ON TABLE S TO PUBLIC ;

PACKAGE AND PLAN PRIVILEGES

GRANT EXECUTE ON PLAN PLANB TO CHARLY ;

COLLECTION PRIVILEGES

GRANT CREATE IN EWSK TO JOHN ;

DATABASE PRIVILEGES

GRANT CREATETAB ON DATABASE DBX TO NANCY ;

USE PRIVILEGES

GRANT USE OF TABLESPACE DBX.TS76 TO TOM ;

SYSTEM PRIVILEGESGRANT CREATEDBC TO ARNOLD ;

REVOKE

USED TO REVOKE PREVIOUSLY GRANTED PRIVILEGES ON AN OBJECT FROM USERS. GENERAL FORMAT OF REVOKE IS SIMILAR TO THAT OF GRANT. REVOKE CAN BE USED TO REVOKE ALL PRIVILEGES EXPLAINED IN THE GRANT COMMAND

EXAMPLES

REVOKE SELECT ON TABLE S FROM CHARLY ;

REVOKE UPDATE ON TABLE S FROM JOHN ;

REVOKE CREATETAB ON DATABASE DBX FROM NANCY ;

COMMIT

COMMIT OPERATES ON A UNIT OF RECOVERY

AFTER EXECUTING THIS STATEMENT

ALL CHANGES WILL BE DONE PERMANENTLY

ROW LOCKS WILL BE RELEASED

DEFAULT COMMIT IS AT PROGRAM TERMINATION

IF AN APPLICATION DETERMINES THAT A UNIT OF WORK IS SUCCESSFUL IT CAN INDICATE THAT TO THE DATABASE MANAGER VIA A COMMIT. THE DATABASE MANAGER CAN MAKE THE CHANGES PERMANENT

CURSORS ARE CLOSED EXCEPT THOSE DECLARED WITH HOLD OPTION

EXAMPLE

UPDATE TABLE SSET STATUS = 20WHERE S# = S1;

COMMIT;

ROLLBACK

A UNIT OF WORK IS UNDONE IF ANY ABNORMAL

CONDITION OCCURS . WHEN THIS STATEMENT

IS EXECUTED

ALL CHANGES IN THAT UNIT OF WORK

WILL BE BACKED OUT

ALL LOCKS ARE RELEASED

ALL OPEN CURSORS ARE CLOSED

WHEN YOU ISSUE A ROLLBACK THEN THE DATABASE MANAGER WILL RE-ESTABLISH THE STATE OF THE DATABASE AT THE LAST COMPLETED UNIT OF WORK

ROLLBACK WILL BE DONE EITHER BY THE PROGRAM OR BY THE SYSTEM.

EXAMPLE

ROLLBACK WORK ;

6. Program Structure

This section gives an over view of a DB2 application program .Different sections to be included in an application are explained briefly.

6.1. Host Variables

6.1.1. Declaring Host Variables

6.2. Indicator Variables

6.3. SQLCA

6.4. Cobol Structure Of SQLCA

6.5. SQLCA Return Codes

6.6. SQLCA Warnings

6.7. Important SQL codes

6.8. Static SQL

6.9. Dynamic SQL

6.10. Example For A DB2 Application Program

PROGRAM STRUCTURE

STRUCTURE OF A PROGRAM THAT ACCESSES DB2

SQLCA

HOST VARIABLE DECLARATIONS

DECLARE TABLE STATEMENTS

DECLARE CURSOR

SQL STATEMENTS WITHOUT FETCH

OPEN CURSOR

FETCH CURSOR

CLOSE CURSOR

DIFFERENT SECTIONS TO BE INCLUDED IN A DB2 PROGRAM ARE SHOWN IN THE ABOVE FIGURE.

IF THE HOST LANGUAGE IS COBOL, THEN HOST VARIABLE DECLARATION, SQLCA, AND DECLARE TABLE STATEMENTS SHOULD BE IN THE WORKING STORAGE SECTION AND CURSOR DECLARATIONS SHOULD BE JUST ABOVE THE PROCEDURE DIVISION. ALL OTHER SECTIONS ARE IN PROCEDURE DIVISION.

Program Structure

Programs that access DB2 are written in a number of host languages - COBOL, PL/1, C , ASSEMBLER , FORTRAN, BASIC etc. These programs can contain SQL statements that retrieves or updates database.

The start and end of SQL statements must be indicated by delimiters. The delimiters used in COBOL are EXEC SQL and END-EXEC.

SQL statements must be coded with in these delimiters. Even if multiple SQL statements appear sequentially, each SQL statement should be indicated by delimiters.

Pre compiler uses delimiters to identify SQL statements from the host language.

EXAMPLE OF USING DELIMITERS IN COBOL

EXEC SQLUPDATE SSET STATUS = 10WHERE CITY = ‘ATHENS’END-EXEC.

HOST VARIABLES

HOST VARIABLES ARE USED TO IDENTIFY THE SYMBOLICNAME OF STORAGE, THAT HAS BEEN DECLARED USING THE APPLICATION PROGRAM LANGUAGE DEFINITION STATEMENT

SQL STATEMENT

SELECT SNAME INTO :TMPNAME WHERE S# = ‘S1’

HOST VARIABLE

HOST VARIABLES ARE OPTIONAL

HOST LANGUAGE VARIABLES IN SQL STATEMENT MUST BE PRECEDED BY A COLON

HOST VARIABLE MUST MATCH COLUMN DATA TYPE

CAN BE USED ANYWHERE A VALUE IS REQUIRED IN AN SQL STATEMENT

EXAMPLE(1)

SQL STATEMENT 1INSERT INTO S( S#, SNAME )VALUES ( ‘S6’ , ‘GEORGE’ )

SQL STATEMENT 2INSERT INTO S( S#, SNAME )VALUES ( :SUPCODE, :SUPNAME )

In SQL statement 1 the values to be inserted are hard coded .Second SQL statement shows the use of host variables in an embedded SQL .This statement could be included in a processing loop with the program’s logic assigning various values to the host variables.

EXAMPLE (2)

SQL STATEMENT

UPDATE SSET STATUS = STATUS * :PERCENTWHERE S# = :SUPCODE

In this example host variables are used to update a table .

DECLARING HOST VARIABLES

THERE ARE TWO METHODS OF HOST VARIABLE DECLARATION

(1) DECLARE HOST VARIABLES IN THE WORKING STORAGE SECTION

(2) EXEC SQL

INCLUDE (member name which contains all host variable declarationsand declare table statements)

END EXEC.

Declaring Host Variables

You can declare all host variables in the working storage section of the COBOL program. The host variable declaration should match with the corresponding column definition

The host variable names must not begin with SQL or EXEC.

Another method of declaring host variables is using the verb INCLUDE. All the host variables are declared in a partitioned dataset member and that member is included in the source program using verb INCLUDE.

INDICATOR VARIABLES

INDICATOR VARIABLE INDICATES THE PRESENCE OF NULL VALUE IN A COLUMN

SELECT SNAME INTO :SUPNAME:SUPNAMINDFROM S

HOST VARIABLE

INDICATOR VARIABLE

INDICATOR VARIABLE IS REQUIRED IF THE SELECTED COLUMNS ALLOWS NULL

IF COLUMN CONTAINS NULL VALUE THEN THE INDICATOR VARIABLE IS SET TO NEGATIVE VALUE, HOST VARIABLE IS UNTOUCHED

INDICATOR VARIABLE IS ASSOCIATED WITH A HOST VARIABLE

Indicator Variables

When the program is to receive a value from a column that allows nulls, the program can get either a value or null. So the program requires two variables, a host variable to receive value and an indicator variable to indicate the presence of null value in the selected column.

If DB2 attempts to indicate the presence of a null and the program does not provide an indicator variable an error occurs.

If the value returned is null then the null indicator indicates that by a negative value and the value in the host variable remains unchanged. The program should have an indicator variable for each column that allows null.

In EXAMPLE1 when the selected column contains a null value then the program logic is coded in such way to tackle it.

Example 2 shows that indicator variables are used for UPDATE operations also. Before updating the table, the indicator variable is made negative and DB2 sets the column to null ignoring the value in the host variable.

Indicator variable should be declared like you declare a host variable. Data type of an indicator variable is SMALLINT and corresponding cobol declaration is given below

01 SUPNAMIND PIC S9(4) COMP.

Examples

1. EXEC SQL SELECT SNAME , CITYINTO :SUPNAME:SUPNAMIND , :PGMCITY FROM S WHERE S# = ‘ S1’END EXEC.

IF SUPNAMIND < 0 PERFORM NONAME-SECTION

ELSEPERFORM NAME-SECTION.

2. IF ( some condition )SUPNAMIND = -1

ELSESUPNAMIND = 0.

EXEC SQL

UPDATE SSET SNAME = :SUPNAM:SUPNAMINDWHERE S# = ‘S1’

END EXEC.

SQLCA ( SQL COMMUNICATION AREA)

THE SUCCESS OR FAILURE OF THE LAST EXECUTED SQL STATEMENT IS DESCRIBED IN SQLCA

PROGRAM STATUS OF EXECUTED SQL

SQLCA

SQL STATEMENTS DB2

AFTER EACH SQL STATEMENT, SQLCA CODES MUST BE CHECKED BY THE PROGRAM TO FIND WHETHER THE SQL WAS SUCCESSFUL OR NOT

SQLCA IS INCORPORATED IN THE PROGRAM USING INCLUDE STATEMENT.

SQLCA

The SQL communication area (SQLCA) is a data structure that must be included in any host language program using SQL .The SQLCA provides a way for DB2 to pass feedback about it’s operations to the program .After executing an SQL DB2 returns via the SQLCA ,codes indicating the execution was successful or identifying errors and special conditions. The program can then test for these codes and react according to their content.

The SQLCA structure contains variables for a number of codes and messages. Programmers can code the necessary structure(explained in next page) , copy it from a source library or have DB2 generate it.

An include statement allows the source program to include SQLCA structure from the copy library and is shown below.

EXEC SQL INCLUDE SQLCAEND EXEC.

COBOL STRUCTURE OF SQLCA

01 SQLCA.05 SQLCAID PIC X(8).05 SQLCABC PIC S9(9) COMP-4.05 SQLCODE PIC S9(9) COMP-4.05 SQLERRM.

49 SQLERRML PIC S9(4) COMP-4.49 SQLERRMC PIC X(70).

05 SQLERRP PIC X(8).05 SQLERRD OCCURS 6 TIMES

PIC S9(9) COMP-4.05 SQLWARN.

10 SQLWARN0 PIC X.10 SQLWARN1 PIC X.10 SQLWARN2 PIC X.10 SQLWARN3 PIC X.10 SQLWARN4 PIC X.10 SQLWARN5 PIC X.10 SQLWARN6 PIC X.10 SQLWARN7 PIC X.

05 SQLEXT.10 SQLWARN8 PIC X.10 SQLWARN9 PIC X.10 SQLWARNA PIC X.10 SQLSTATE PIC X(5).

MOST IMPORTANT SQLCA CODES ARE SQLCODE AND SQLWARN0

SQLCA RETURN CODES

INTEGER CHAR(1)CONDITION SQLCODE SQLWARN0 REQUEST STATUS

ERROR <0 FAILED

WARNING >0 & <>100 OR ‘W’ SATISFIED WITH SPECIAL

CONDITION

NOT FOUND +100 DATA NOTFOUND

SUCCESS 0 AND ‘ ‘ SUCCESS

IF SQLCODE CONTAINS A NEGATIVE VALUE THEN IT IS AN ERROR

ALL POSITIVE SQLCODES NOT EQUAL TO 100 ARE CONSIDERED WARNINGS

A ‘W’ IN SQLWRN0 INDICATES A WARNING EVEN IF SQLCODE = 0.

SQLCA WARNINGS

SQL WARNING DESCRIPTION

SQLWARN0 THIS FIELD IS BLANK IF ALL SQL WARNINGS FROM SQLWARN1 TO SQLWARNA ARE BLANKS.CONTAINS ‘W’ IF ONE OR MORE SQL WARNINGSCONTAINS W.

SQLWARN1 CONTAINS W IF THE VALUE OF A STRING COLUMN WAS TRUNCATED WHEN ASSIGNED TO HOSTVARIABLE.

SQLWARN2 CONTAINS W IF NULL VALUES WERE ELIMINATED FROM THE ARGUMENT OF A COLUMN FUNCTION

SQLWARN3 CONTAINS W IF THE NUMBER OF RESULT COLUMNSIS LARGER THAN THE NUMBER OF HOST VARIABLES.

SQLWARN4 CONTAINS W IF A PREPARED UPDATE OR DELETE STATEMENT DOES NOT INCLUDE A WHERE CLAUSE.

SQLWARN5 CONTAINS W IF THE SQL STATEMENT WAS NOTEXECUTED BECAUSE IT IS NOT A VALID SQLSTATEMENT IN DB2 FOR MVS/ESA.

SQLCA WARNINGS…..

SQL WARNING DESCRIPTION

SQLWARN6 CONTAINS W IF THE ADDITION OF A MONTH OR YEAR DURATION TO A DATE OR TIMESTAMP VALUE RESULTS IN AN INVALID DAY. AN INVALID DAY (FOR EXAMPLE, JUNE 31). INDICATES THAT THE VALUE OFTHE DAY WAS CHANGED TO THE LAST DAY OF THEMONTH TO MAKE THE RESULT VALID.

SQLWARN7 CONTAINS A W IF ONE OR MORE NON ZERO DIGITSWERE LIMITED FROM THE FRACTIONAL PART OFA NUMBER USED AS THE OPERAND OF A DECIMALMULTIPLY OR DIVIDE OPERATION.

SQLWARN8 CONTAINS A W IF A CHARACTER THAT COULD NOTBE CONVERTED WAS REPLACED WITH A SUBSTITUTE CHARACTER.

SQLWARN9 CONTAINS A W IF ARITHMETIC EXCEPTIONS WEREIGNORED DURING COUNT DISTINCT PROCESSING.

SQLWARNA CONTAINS A W IF AT LEAST ONE CHARACTER FIELDOF THE SQLCA OR THE SQLDA NAMES OR LABELS ISINVALID DUE TO A CHARACTER CONVERSION ERROR.

Important SQL codes

-102 LITERAL STRING IS TOO LONG. STRING BEGINS string

-107 THE NAME name IS TOO LONG. MAXIMUM ALLOWABLE SIZE IS size

-117 THE NUMBER OF INSERT VALUES IS NOT THE SAME AS THE NUMBER OF OBJECT COLUMNS

-119 A COLUMN IDENTIFIED IN A HAVING CLAUSE IS NOT INCLUDED IN THE GROUP BY CLAUSE

-125 AN INTEGER IN THE ORDER BY CLAUSE DOES NOT IDENTIFY A COLUMN OF THE RESULT

-150 THE OBJECT OF THE INSERT, DELETE, OR UPDATE STATEMENT IS A VIEW FOR WHICH THE REQUESTED OPERATION IS NOT PERMITTED

-204 name IS AN UNDEFINED NAME

-205 column-name IS NOT A COLUMN OF TABLE table-name

-303 A VALUE CANNOT BE ASSIGNED TO OUTPUT HOST VARIABLE NUMBER position-number BECAUSE THE DATA TYPES ARE NOT COMPARABLE

-401 THE OPERANDS OF AN ARITHMETIC OR COMPARISON OPERATION ARE NOT COMPARABLE

-407 AN UPDATE OR INSERT VALUE IS NULL, BUT THE OBJECT COLUMN column-name CANNOT CONTAIN NULL VALUES

-501 THE CURSOR IDENTIFIED IN A FETCH OR CLOSE STATEMENT IS NOT OPEN

-502 THE CURSOR IDENTIFIED IN AN OPEN STATEMENT IS ALREADY OPEN

-503 A COLUMN CANNOT BE UPDATED BECAUSE IT IS NOT IDENTIFIED IN THE UPDATE CLAUSE OF THE SELECT STATEMENT OF THE CURSOR

-504 THE CURSOR NAME cursor-name IS NOT DEFINED

-540 THE DEFINITION OF TABLE table-name IS INCOMPLETE BECAUSE IT LACKS A PRIMARY INDEX OR A REQUIRED UNIQUE INDEX

-551 auth-id DOES NOT HAVE THE PRIVILEGE TO PERFORM OPERATION operation ON OBJECT object-name

-603 A UNIQUE INDEX CANNOT BE CREATED BECAUSE THE TABLE CONTAINS ROWS WHICH ARE DUPLICATES WITH RESPECT TO THE VALUES OF THE IDENTIFIED COLUMNS

-623 A CLUSTERING INDEX ALREADY EXISTS ON TABLE table-name

-661 INDEX index-name CANNOT BE CREATED ON PARTITIONED TABLE SPACE tspace-name BECAUSE THE NUMBER OF PART SPECIFICATIONS IS NOT EQUAL TO THE NUMBER OF PARTITIONS OF THE TABLE SPACE

-672 OPERATION DROP NOT ALLOWED ON TABLE table_name

-719 BIND ADD ERRORUSING auth-id AUTHORITYPACKAGE package-nameALREADY EXISTS

-805 DBRM or PACKAGE NAME location-name.collection-id.dbrm-name.consistency -token NOT FOUND IN PLAN plan-name. REASON reason

-811 THE RESULT OF AN EMBEDDED SELECT STATEMENT IS A TABLE OF MORE THAN ONE ROW, OR THE RESULT OF THE SUBQUERY OF A BASIC PREDICATE IS MORE THAN ONE VALUE

-904 UNSUCCESSFUL EXECUTION CAUSED BY AN UNAVAILABLE RESOURCE. REASON reason-code, TYPE OF RESOURCE resource-type, AND RESOURCE NAME resource-name

-911 THE CURRENT UNIT OF WORK HAS BEEN ROLLED BACK DUE TO DEADLOCK OR TIMEOUT. REASON reason-code, TYPE OF RESOURCE resource-type, AND RESOURCE NAME resource-name

-913 UNSUCCESSFUL EXECUTION CAUSED BY DEADLOCK OR TIMEOUT. REASON CODE reason-code, TYPE OF RESOURCE resource-type, AND RESOURCE NAME resource-name

CODING AIDS

WHENEVER STATEMENT

EXEC SQLWHENEVER Condition ActionEND-EXEC

CONDITION:SQLERROR

-- NEGATIVE SQLCODESQLWARNING

-- POSITIVE SQLCODE ( NOT +100 )-- OR SQLWARN0 = ‘W’

NOT FOUND-- SQLCODE = +100

ACTION:GO TO :SECTA

-- CONTROL TRANSFERRED TO STATEMENT LABELED SECTA

CONTINUE-- PROGRAM CONTINUES WITH NEXT STATEMENT-- USED TO CANCEL THE EFFECT OF PRIOR WHENEVER

PHYSICAL PLACEMENT OF WHENEVER STATEMENT DETERMINES THE SQL STATEMENTS UNDER IT’S EFFECT

THE USE OF COLON BEFORE THE LABEL IS OPTIONAL

‘’ GO TO ‘’ AND ‘’ GOTO ’’ ARE EQUIVALENT

Whenever Statement

WHENEVER statements help programmers to avoid checking SQLCODE after every SQL statement. WHENEVER statements are SQL STATEMENTS that can be embedded in one or more times in the host language program for branching to a paragraph depending on the content of SQLCODE.

Each WHENEVER statement applies to all of the SQL statements that follow it in the program listing, regardless of order in which the statements are actually executed. This happens because COBOL precompiler puts appropriate branching instruction after every SQL statement that follows the whenever statement.

WHENEVER statements can be used for three different conditions and these are similar to IF THEN statements. IF SQLcode satisfies some condition then the program performs the branching .

EXAMPLE

EXEC SQLWHENEVER NOT FOUND CONTINUEEND-EXEC

EXEC SQLWHENEVER SQLERROR PERFORM ERR-SECTIONEND-EXEC

EXEC SQLWHENEVER SQLWARNING PERFORM WARN-SECTIONEND-EXEC

INCLUDE STATEMENT

THE INCLUDE STATEMENT INSERTS DECLARATIONS OR CODE INTO A SOURCE PROGRAM.

SOURCE PROGRAM SQLCA (TO BE INCLUDED IN SOURCE PROGRAM )

01SQLCAEXEC SQL 05 SQLCAID PIC X(8).

05 SQLCABC PIC S9(9) COMP-4. INCLUDE SQLCA

END-EXEC.

THE INCLUDE STATEMENT INSERTS SOURCE CODE INTO A SOURCE PROGRAM AT PRE COMPILE TIME.

THE INCLUDE STATEMENT CANNOT REFER TO SOURCE STATEMENTS THAT THEMSELVES CONTAIN INCLUDE STATEMENTS.

USING CURSORS

PROCESSING MULTIPLE ROWS

QUERY: SELECT STATUS, CTTY INTO :RANK, :CITYFROM S WHERE STATUS < 30 ;

STATUS CITY

2 LONDON10 PARIS20 LONDON

RANK CITY

STATUS CITY


RANK CITY

STATUS CITY


RANK CITY

Processing Multiple Rows

In previous example the result of the query gives multiple rows. But there is no method to determine the number of rows satisfying the condition before actually receiving data from DB2.Therefore it is not possible to allocate storage in the application program to receive an entire set of data.

When we are using host variables for retrieving data and if the result is a single row the query will work and SQL return code will be set to zero. But in the given example the result of the query gives multiple rows and the host language can deal with only at a time Now the program is in error, SQLCODE will be set to a negative value and the values of the host variables will be unpredictable.

DB2 provides the use of cursors to process SETS of data. The cursor is used to retrieve all rows in the SET one by one. Each fetch of the cursor retrieves the next row in the set of data that meets the condition.

SELECT WITH FETCH

DEFINE A CURSOREXEC SQL

DECLARE CURSOR K10 FORSELECT SNAME, CITY DEFINITIONFROM SWHERE STATUS < 30END-EXEC

OPEN THE CURSOREXEC SQL

OPEN K10END-EXEC

FETCH RESULT ROWS ONE AT A TIMEEXEC SQL EXECUTION

FETCH K10 INTO :SUPNAME, :CITYEND-EXEC

CLOSE CURSOR WHEN FINISHEDEXEC SQL

CLOSE K10END-EXEC

THE DECLARE CURSOR STATEMENT RELATES A CURSOR TO A SELECT STATEMENT

OPEN CURSOR STATEMENT GENERATES EXECUTABLE CODE.

FETCH CURSOR STATEMENT RETRIEVES A ROW FROM A SET OF DATA

CLOSE CURSOR STATEMENT DEACTIVATES THE CURSOR

Select With Fetch

DECLARE cursor statement defines a cursor with the specified name with an associated query as specified by the select that forms part of that declare. The declare cursor statement is not an executable code, but a purely declarative statement. A program can use any number of DECLARE CURSOR statements, and each of which must be of a different name.

Open cursor statement generates executable code. The select clause used in the DECLARE CURSOR statement is effectively executed when the cursor is opened. This is done using the current value of the host variable (if used).This executable code will allow subsequent fetch statements to access the set of data that meets the definition of the DECLARE CURSOR‘s underlying SELECT statement. Opening the cursor is a must and DB2 will not open it on the first fetch.

The FETCH statement will retrieves a row of data from the set made accessible by the open statement. Data is retrieved in host variables specified after the INTO clause of FETCH statement. After the first FETCH statement which retrieves the first row, the cursor will be advanced to the next row during the second FETCH operation and then assigns values from that row to host variables.

After retrieving the required rows the CURSOR can be closed. The CLOSE CURSOR statement releases the cursor from the set of data.

UPDATE USING A CURSOR

EXEC SQLDECLARE CURSOR K10 FORSELECT SNAME, CITY FROM SWHERE STATUS = :RANKFOR UPDATE OF CITYEND-EXEC

EXEC SQLOPEN K10

END-EXEC

EXEC SQLFETCH K10 INTO :SUPNAME, :CITY

END-EXEC

EXEC SQLUPDATE SSET CITY = :NEWCITYWHERE CURRENT OF K10

END-EXEC

EXEC SQLCLOSE K10

END-EXEC

DECLARE CURSOR HAS AN ADDITIONAL FOR UPDATE OF CLAUSE.

DECLARE, OPEN, FETCH and CLOSE CURSOR LOGIC IS NOT CHANGED

UPDATE WHERE CURRENT OF cursor name UPDATES THE ROW PRESENTLY IDENTIFIED BY THE CURSOR

Update Using A Cursor

The usual logic of cursors is used for updating a row which is present in the set of data, satisfying the select statement in the DECLARE CURSOR. The columns that may be updated are specified using FOR UPDATE OF clause in the DECLARE CURSOR statement.

The update operation is done after fetching a row from the SET of data. This type of update is useful where the retrieved row is required for the program before updating it. UPDATE WHERE CURRENT OF CURSOR clause updates the row where the cursor is presently positioned. The next row can be updated only after issuing another FETCH.

Requirement of specifying FOR UPDATE OF clause for updating a table using CURSORS depends on the pre compiler option given. If pre compiler NOFOR option is specified then FOR UPDATE OF clause is not required. If NOFOR is not specified FOR UPDATE OF CLAUSE is required and an attempt to update a column not mentioned in that column will fail at run time.

DELETE USING A CURSOR

EXEC SQLDECLARE CURSOR K10 FORSELECT SNAME, CITY FROM SWHERE STATUS = :RANKFOR UPDATE OF CITY

END-EXEC

EXEC SQLOPEN K10

END-EXEC

EXEC SQLFETCH K10 INTO :SUPNAME, :CITY

END-EXEC

EXEC SQLDELETE FROM SWHERE CURRENT OF K10

END-EXEC

EXEC SQLCLOSE K10

END-EXEC

THE DECLARE, OPEN, FETCH and CLOSE CURSOR LOGIC IS NOT CHANGED

DELETE WHERE CURRENT OF cursor DELETES THE ROW PRESENTLY POSITIONED BY THE CURSOR

THIS FORM OF DELETE WILL BE USED IF THE DATA CONTAINED IN A ROW IS NEEDED BY THE APPLICATION BEFORE IT IS DELETED.

STATIC SQL

PLAN TO SELECT DATA

PROGRAM PLAN

DB2

PROGRAM HANDLES THE RESULT

STATEMENTPROGRAMMER KNOWS THE SQL STATEMENT TO BE USED AND ALWAYS DOES THE SAME FUNCTION ON THE SAMETABLES AND COLUMNS.

BIND ON ALL SQL STATEMENTS BEFORE PROGRAM EXECUTION BUILDS A STORED PLAN

* SELECT CALL RESULT

SELECT

TABLE

AUTHORIZATION HELD BY THE PLAN BINDER

DYNAMIC SQL

PLAN TO EXECUTE USER’S REQUEST

PROGRAM PLAN PREPARE DB2

EXECUTE

CALL EXECUTE TABLE

RESULT

PROGRAM HANDLES THE RESULT

STATEMENT

SQL STATEMENTS ARE PREPARED AT RUN TIME ANDEXECUTED. TARGET TABLE OR COLUMN CAN BE SPECIFIED AT RUN TIME

BIND ON SINGLE STATEMENT AT STATEMENT EXECUTION ACCESS STRATEGY NOT SAVED

AUTHORIZATION

HELD BY THE PROGRAM EXECUTOR

Example For Dynamic SQL

01 STMT49 LEN PIC S9(4) COMP.49 TEXT PIC X(200).

01 X PICX(6).01 Y PICX(6).01 Z PIC X(6).

………………………………………

EXEC SQL DECLARE SS STATEMENT END-EXEC

EXEC SQL DECLARE CC CURSOR FOR SS END-EXEC…………………………MOVE WS-TEXT TO TEXT:MOVE LENGTH-OF-TEXT TO LEN

(SELECT CL1,CL2,CL3 FROM T1 WHERE CL1 = 1932)

EXEC SQL PREPARE SS FROM :STMT END-EXECEXEC SQL OPEN CC END-EXEC

EXEC SQL FETCH CC INTO :X, :Y, :Z END-EXEC

( repeat fetch until sqlcode 100)…………………………………….

EXEC SQL CLOSE CC END-EXEC

Example For A Db2 Application Program

IDENTIFICATION DIVISION.******************************************************************* IDENTIFICATION DIVISION. * * * ****************************************************************** PROGRAM-ID. SXD11018. ****************************************************************** * * ****************************************************************** ENVIRONMENT DIVISION. ****************************************************************** * * * ENVIRONMENT DIVISION. * * * ****************************************************************** CONFIGURATION SECTION. ******************************************************************** CONFIGURATION SECTION. * * * ****************************************************************** SPECIAL-NAMES. DECIMAL-POINT COMMA. INPUT-OUTPUT SECTION. ****************************************************************** * * * INPUT-OUTPUT SECTION. * * * ****************************************************************** FILE-CONTROL. DATA DIVISION. ****************************************************************** * * * DATA DIVISION. * * * ****************************************************************** FILE SECTION. ****************************************************************** * * * FILE SECTION. ** ***********************************************************

WORKING-STORAGE SECTION. ****************************************************************** * * * WORKING-STORAGE SECTION. * * * *******************************************************************-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*- * * DB2-COMMUNICATION-AREA DECLARATIONS * *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*- EXEC SQL INCLUDE SQLCA END-EXEC. *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*- * * SQL-TABLE DECLARATIONEN * *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-EXEC SQL INCLUDE VT11018 ( OUTPUT OF DCLGEN ) END-EXEC. / ………………………………………………………………………………………………………………………………( WORKING STORAGE

VARIABLES ) ……………………………………………………………… LINKAGE SECTION. ****************************************************************** * L I N K A G E S E C T I O N * ****************************************************************** * ………………………………………………………………….……………………………………………………………………………………………………………………………

*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*- * * SQL-CURSOR DECLARATIONS * *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*- EXEC SQL DECLARE T11018_ALL_ROW CURSOR FOR SELECT

TAB_INDEX , DAHWV , DAHWB , DART FROM VT11018 ORDER BY TAB_INDEX END-EXEC. PROCEDURE DIVISION ****************************************************************** * * * PROCEDURE DIVISION * * * ****************************************************************** * ************************************************************************************************************************************ * ……………………………………………………….……………………………………………………….……………………………………………………… / ****************************************************************** 8100-OPEN-T11018-CURSOR SECTION. ****************************************************************** EXEC SQL OPEN T11018_ALL_ROW END-EXEC ******************************************************************…………………………………………………………….…………………………………………………………….

……………………………………………………………..………………………………………………………………8100-FETCH-T11018-ROW SECTION. ( THIS SECTION SHOULD BE IN A

LOOP TO FETCH ALL ROWS) ****************************************************************** EXEC SQL FETCH T11018_ALL_ROW INTO :TAB-INDEX , :DAHWV , :DAHWB , :DART END-EXEC ******************************************************************

………………………………………………………….……………………………………………………………………………………………………………………………………………………………………………………………. 8100-CLOSE-T11018-CURSOR SECTION. ****************************************************************** EXEC SQL CLOSE T11018_ALL_ROW END-EXEC STOP RUN.

7. Program Preparation

This chapter explains the steps involved in executing a db2 application program.Control information required for each step and examples are also providedThe topics discussed in this chapter are

7.1. Steps In Program Preparation

7.2. DCLgen (Declarations Generator )

7.3. Precompile

7.4. Bind

7.4.1. Binding A DBRM To A Package

7.4.2. Binding An Application Plan

7.5. Compile And Linkedit

7.6. Overview Of DB2 Application Program Preparation And Execution

7.7. Associating Load Modules And Packages

PROGRAM PREPARATION

STEPS IN PROGRAM PREPARATION

DCLGEN

PROGRAM PRE COMPILE

BIND

COMPILE AND LINK EDIT

EXECUTION

DB2 APPLICATION PROGRAM SHOULD GO THROUGH ALL THE ABOVE STEPS.

DCLGEN (DECLARATIONS GENERATOR )

INPUT OUTPUT

DECLARE TABLE STATEMENT

CONTROL STATEMENTSWHICH INCLUDE TABLE OR DCLGENVIEW NAME AND NAME OFTHE HOST LANGUAGE HOST LANGUAGE

DATA STRUCTURE

DCLGEN USES DB2CATALOG TABLES

DCLGEN SHOULD BE DONE BEFORE PRE COMPILING THE SOURCE MODULE

DCLGEN GENERATES BOTH DECLARE TABLE STATEMENT AND DATA STRUCTURE IN THE SPECIFIED HOST LANGUAGE.

DECLARE TABLE STATEMENT USED FOR APPLICATION PROGRAM DOCUMENTATION AND PRELIMINARY SYNTAX CHECKING FOR THE PRE COMPILER

USE DCLGEN OR CODE DECLARE TABLE AND HOST LANGUAGE DATA STRUCTURE MANUALLY

DCLGEN (Declarations Generator )

The DECLARATIONS GENERATOR supplied with DB2 produces DECLARE TABLE statements for tables and views. It also generates host language data structure that corresponds to the DB2 tables and views to be accessed by the program. The output of DCLGEN will be created in a partition dataset member This member should be included in the working storage section of the application program using INCLUDE statement.

The purpose of having DECLARE TABLE statement in the source code is to allow the pre compiler to check the syntax of the SQL statements referring to the tables and views. Having the table and view declarations in the source code allows the pre compiler to uncover syntactical errors, which otherwise would not be found until DB2 binds the plan or package.

Host language data structure produced by DCLGEN, is the HOST LANGUAGE DECLARATIONS of tables or views. These can be used as host variables in the application program. DCLGEN prevents us from manually coding host variable declarations and declare table statements.

EXAMPLE

INPUT FOR DCLGEN

DCLGEN TABLE(S)LIBRARY(NTCI.PTAB.DCL(S))ACTION(REPLACE)LANGUAGE(COBOL)STRUCTURE(S)QUOTE

OUT PUT FROM DCLGEN IN NTCI.PTAB.DCL(S)

****************************************************************** * DCLGEN TABLE(S) * * LIBRARY(NTCI.PTAB.DCL(S)) * * ACTION(REPLACE) * * LANGUAGE(COBOL) * * STRUCTURE(S) * * QUOTE * * IS THE DCLGEN COMMAND THAT MADE THE FOLLOWING * STATEMENTS * ******************************************************************

EXEC SQL DECLARE S TABLE(S# CHAR(5) NOT NULL,SNAME CHAR(20),NOT NULL WITH DEFAULTSTATUS SMALLINT NOT NULL WITH DEFAULT,CITY CHAR(15) NOT NULL WITH DEFAULT) END-EXEC

****************************************************************** * COBOL DECLARATION FOR TABLE VT11010 * ******************************************************************

01 S.10 S# PIC X(5).10 SNAME PIC X(20).10 STATUS PIC S9(4) COMP.10 CITY PIC X(15).

******************************************************************* THE NUMBER OF COLUMNS DESCRIBED BY THIS DECLARATION IS 4*******************************************************************

PRECOMPILE

SOURCE MODULE

SOURCE LISTINGDIAGNOSTICS PRE COMPILECROSS REFERENCES

MODIFIEDSOURCE CODE DBRM

(CONTAINS (CONTAINS CONSISTENCY CONTOKEN )

TOKEN)

PRE COMPILER INPUTHOST LANGUAGE PROGRAM WHICH CONTAINS SQL STATEMENTS

SQL STATEMENTS ARE COMMENTED OUT ARE REPLACED BY HOST LANGUAGE CALL STATEMENTS

PRE COMPILER OUTPUT MODIFIED SOURCE CODE WHICH CONTAINS PRE COMPILER

CONSISTENCY TOKEN (CONTOKEN) WHICH IS AN INTERNAL REPRESENTATION OF TIMESTAMP.

DATABASE REQUEST MODULE WHICH CONTAINS EDITED FORM OF SQL STATEMENTS AND CONSISTENCY TOKEN

ERROR MESSAGES AND OTHER DIAGNOSTIC INFORMATION

Pre Compile

DB2 application programs include SQL statements and you cannot compile those programs until you change the SQL statements into the language recognized by your compiler. Hence you must use a pre compiler whose function is to analyze the host language source module, stripping all SQL statements it finds and replacing them by host language call statements. PRE COMPILER also creates a DBRM from the SQL statements it encountered. DBRM communicates your SQL requests to DB2 during BIND process.

One DBRM is created for a program, the name of the DBRM and program will be the same. DBRM contains SQL statements and host variable information extracted from the source program. The DBRM also contains a consistency token that identifies the program and ties the DBRM to the modified source statements by using the same consistency token present in the modified source code.

The pre compiler does a syntax checking using the definition given by the DECLARE TABLE statement on all SQL statements in the program. Pre compiler gives error , warnings and other diagnostic messages depending on the result of syntax checking .

BIND

DBRMS DIRECTLY BOUND TO THE PLAN

INPUT OUTPUT

DBRM1 BIND PLAN

DBRM2

DBRMS BOUND TO THE PACKAGE AND PACKAGES BOUND TO THE PLAN

DBRM1 BIND PACKAGE1

BIND PLAN

DBRM2 BIND PACKAGE2

THERE ARE TWO TYPES OF BIND BIND PACKAGE BIND PLAN

BIND

BIND CONVERTS HIGH LEVEL SQL STATEMENTS PRESENT IN DBRM TO EXECUTABLE MACHINE INSTRUCTION

BIND THE DBRM TO A PLAN OR PACKAGE BEFORE EXECUTING THE APPLICATION PROGRAM.

BIND INVOLVES

CHECKING THE STATUS OF THE REFERENCED OBJECTS TO DETERMINE IF AN SQL STATEMENT IS EXECUTABLE

CREATING AN OPTIMIZED FORM OF THE SQL STATEMENTSFOR IMPROVED PERFORMANCE AND COMPACTNESS

IDENTIFYING MOST EFFICIENT PATH FOR EACH SQL STATEMENT

BIND CHECKS THE AUTHORIZATION TO PERFORM OPERATIONS REQUESTED BY THE SQL STATEMENT

THE CONSISTENCY TOKEN PRESENT IN THE DBRM WILL BE CARRIED FORWARD TO PACKAGE AND PLAN

Bind

The out put of the precompiler contains extracted SQL statements from the source module. But DB2 has to do the syntax checking and should determine the best access strategy for each SQL. DB2 records all these information in the PACKAGE.

If a DBRM is thought of as an ‘SQL source module’ then the package produced by binding that DBRM can be thought of as the corresponding object module. In other words, a package consists of a set of internal control structures , representing the compiled form of the original SQL statements in the corresponding DBRM

Each package is assigned to exactly one collection when it is bound. When you bind a package, you specify the collection to which the package belongs. The collection is not a physical entity, and you do not create it; the collection name is merely a convenient way of referring to a group of packages. Usually all of the packages used in a given application would be assigned to the same collection

There are two types of bind. First method is to bind DBRMS to an application plan. In the second method DBRMS are bound to the package and packages to the PLAN. Plan contains pointers to the packages.

Bind examines the SQL statements in the input DBRM an checks whether all the necessary elements of a statement are present and syntactically correct. It also checks that the individual binding the plan is authorized to perform the operations requested by the SQL statement.

Optimizer component of bind interrogates catalog tables, chooses the access path and generates the machine code calls needed to execute the statement.

BINDING A DBRM TO A PACKAGE

DBRM CATALOG

PACKAGE BIND LISTINGDIAGNOSTICS

PACKAGE

EACH PACKAGE CONTAINS ONLY ONE DBRM.

PACKAGES ARE OPTIONAL, ALL MEMBERS CAN BE DIRECTLY BOUND TO A SINGLE PLAN

INPUT TO THE PACKAGE BIND IS DBRM AND OUTPUT IS THE PACKAGE.

PACKAGE MUST BE BOUND TO THE PLAN

CON-TOK FROM THE DBRM WILL BE CARRIED ON TO PACKAGE

Binding A DBRM To A Package

Bind Package Is Explained Using The Following Example

BIND PACKAGE (EWSK) -MEMBER (SXD11010) -OWNER (AM1240) -QUALIFIER (SYSADMK ) -VALIDATE (BIND) -EXPLAIN (NO) -ISOLATION (CS) -RELEASE (COMMIT) -ACTION (REPLACE)

When you BIND a package specify the collection to which the package belongs. The collection is not a physical entity and you do not create it.

In the example collection name is EWSK and the package name produced by this bind is EWSK.SXD11010

The owner of the package is AM1240.The owner of an object has all privileges on that object. If no value is entered the default is the use of the primary AUTHID of the binder.

The qualifier parameter will be used as the qualifier of all unqualified tables and views referenced in the application program.

Validate parameter is used to specify the method DB2 will use to validate the package or plan. Validation can be performed during bind or when the program runs, indicated by the choices of BIND or RUN with the VALIDATE parameter.VALIDATE (RUN) is the default value.

EXPLAIN indicates whether to provide information to the user about the access strategy decided by the bind. Default is EXPLAIN(NO)

ACTION parameter indicates whether the package is new or a replacement. ACTION (ADD) will result in an error if the object already exists. The default value of REPLACE will add the object or replace it if it already exists.

ISOLATION specifies the locking strategy while using cursors. Default is RR (repeatable read) , can be over ridden using CS (cursor stability): For more information on ISOLATION parameter please refer chapter 9

RELEASE parameter indicates when the locks should be released while using a cursor.

BINDING AN APPLICATION PLAN

LIST OF PACKAGESOR

DBRMSOR

BOTH

PLAN BIND LISTINGDIGNOSTICMESSAGES

PLAN

DBRMS CAN BE BOUND TO A PLAN

A LIST OF PACKAGES CAN BE BOUND TO A PLAN

DBRMS AND PACKAGES TOGETHER CAN BE BOUND TO A SINGLE APPLICATION PLAN

PLAN CONTAINS POINTERS TO THE PACKAGES

Binding An Application Plan

BIND PLAN IS EXPLAINED USING THE FOLLOWING EXAMPLE

BIND PLAN (A610 ) -MEMBER(W41600, w710009) -OWNER(SYSADM) -QUALIFIER(SYSADM) -PKLIST(EWS.A61000 -

EWS.SXD11053 , -EWSA.ANLZDB2) -

ACTION(REPL) RETAIN -VALIDATE(BIND) -ISOLATION(CS) -CACHESIZE(0)

In the above example name of the plan is A610, two DBRMS, and three packages are bound to the plan.

Parameters used in this example have the same meaning as in the bind package statement.

The parameter ACTION indicates whether a new package is to be added or replaced. ACTION(REPL)RETAIN can be used only for BIND PLAN. RETAIN parameter preserves EXECUTE privileges when you replace the plan. If RETAIN is specified then those users who had been using the plan earlier will have the authority to use it after the bind.

Determines the size (in bytes) of the authorization cache acquired in the EDM pool for the plan. At run time, the authorization cache stores user IDs authorized to run. Consulting the cache can avoid a catalog lookup for checking authorization to run the plan.

COMPILE AND LINKEDIT

MODIFIED SOURCE MODULE (CONTAINS CONTOKEN)

COMPILER

OBJECT MODULE

OTHERLINK EDITOR OBJECT MODULES

LOAD MODULE

(CONTAINS CONTOKEN)

MODIFIED SOURCE FROM THE PRE COMPILER IS COMPILED USING HOST LANGUAGE COMPILER WHICH PRODUCES OBJECT MODULE.

LINKAGE EDITOR IS USED TO MAKE AN EXECUTABLE LOAD MODULE WHICH CONTAINS MAIN PROGRAM, SUB PROGRAMS, LANGUAGE INTERFACE ROUTINES, AND SYSTEM ROUTINES.

TIMESTAMP PRESENT IN THE MODIFIED SOURCE IS CARRIED ON TO THE LOAD MODULE

OVERVIEW OF DB2 APPLICATION PROGRAM PREPARATION AND EXECUTION

SOURCE MODULE

MODIFIED SOURCE PRECOMPILER DBRM MODULE

COMPILER BIND

OBJECT PACKAGEMODULE

OTHERLINKAGE OBJECT LIST OF BIND EDITOR MODULES PACKAGES

LOAD LOAD MODULE APPLICATIONMODULE PLAN

PLAN / PACKAGES

MAIN MEMORY

ASSOCIATING LOAD MODULES AND PACKAGES

CT CTPRE COMPILE

MODIFIED SOURCE DBRM

CT CT

LOAD MODULE PLAN

CONTOKENS SHOULD MATCH

TO EXECUTE

Associating Load Modules And Packages

During PRECOMPILE a CONSISTENCY TOKEN is placed in both the modified source and the DBRM. When DBRM is directly bound to the plan then the CONSISTENCY TOKEN is carried on to the plan from the DBRM. When DBRM is bound to the package then the same CONSISTENCY TOKEN will be present in the package and plan contains pointers to the package. An executable load module can be linked to it’s plan or package using the CONSISTENCY TOKEN field present in them. CONSISTENCY TOKEN is used to ensure that the resultant load module and package were derived from the same original source.

Assume that the plan of an application program contains only DBRMS. When this program executes the CONSISTENCY TOKEN present in the load module and the corresponding DBRM should be the same . Otherwise the program will not be executed and gives an SQLCOSE OF -805.

Now the DBRM of an application program is bound to the package and a set of packages are bound to the plan. When this program is executed the load module and the package which the program wants to execute should have the same CONSISTENCY TOKEN, failure of this will give an SQLCODE -805.

8. Security Features

DB2 provides data integrity by using different security mechanisms. Data access is controlled by using authorization ID’s and privileges given to that ID. This chapter briefly explains these security features and DB2’s referential integrity support.

8.1. Privileges

8.2. Referential Integrity

8.2.1. DB2 Enforcement Of Referential Integrity

8.2.2. Referential Integrity Enforcement Rules

8.2.3. Example For Referential Integrity Violation

8.3. Database Recovery In Case Of Failure

8.3.1. Unit Of Recovery

8.3.2. Data Recovery

SECURITY FEATURES

SECURITY IN DATABASE MEANS THE PROTECTION OF ALL OBJECTS IN DATABASE AGAINST UNAUTHORIZED DISCLOSURE, ALTERATION OR DESTRUCTION.

DB2 USES TWO INDEPENDENT FEATURES TO PROVIDE SECURITY TO IT’S OBJECTS

THE AUTHORIZATION SUB SYSTEM THE VIEW MECHANISM

THE SYSTEM ADMINISTRATOR PROVIDES AUTHORIZATION ID’S TO IT’S USERS. THIS ID IS USED TO LOG ON TO THE SYSTEM AND THE ACTIVITIES USER CAN PERFORM IN DB2 DEPENDS ON THE PRIVILEGES GRANTED TO THIS ID.

THERE ARE TWO TYPES OF AUTHORIZATION ID’S

PRIMARY AUTHORIZATIONS IDS SECONDARY AUTHORIZATION IDS

VIEW MECHANISM CAN BE USED TO PROTECT SENSITIVE DATA FROM USERS BY CREATING A VIEW ON COLUMNS OF THE BASE TABLE THAT ARE NOT SENSITIVE. NOW THE USER ARE ALLOWED TO USE THIS VIEW , PROTECTING SENSITIVE DATA.

Security Features

Authorization ID’S are provided to users of DB2 to prevent unauthorized use of DB2 objects. Users are known to DB2 by this authorization identifier given by the system administrator and it is user’s responsibility to identify themselves to by supplying that ID when they sign on to the system.

Two types of authorization ID’s DB2 uses to control and track system utilization are primary and secondary AUTHIDs.

Each individual is assigned a PRIMARY AUTHID that is used to sign on to the system. Generally it is the primary authorization ID that identifies a process in DB2. When unqualified tables, views, indexes are used in the application program, this AUTHID becomes the qualifier of the object. The operations which can be performed by this AUTHID depends on the privileges granted to it by system administrator or other users.

System administrator may provide a secondary authid to a group of developers who need a set of privileges associated with that id. Now the user has all the privileges of both primary and secondary authid. The secondary authorization ID is optional .

A user can use DB2 under either a primary AUTHID or secondary AUTHID or both. Suppose you are using primary id and want to shift to secondary authid for some operation to perform . This shift can be achieved by using the command

SET CURRENT SQLID = ‘ (name of secondary id)’.

PRIVILEGES

SYSTEM ADMINISTRATOR DECIDES WHICH SPECIFIC PRIVILEGE SHOULD BE GIVEN TO WHICH SPECIFIC USERS

DATABASE ADMINISTRATOR HAS IMPLICIT RIGHT TO GRANT OR REVOKE PRIVILEGES FROM THE USER.

DATABASE ADMINISTRATOR CAN GIVE INDIVIDUAL OR A COLLECTION OF PRIVILEGES TO USERS

CREATOR OF AN OBJECT HAS IMPLICIT RIGHT TO DROP OR ALTER THE OBJECT

SYSTEM ADMINISTRATOR HAS THE AUTHORITY TO TAKE ANY POSSIBLE ACTION WITHIN THE DB2 SYSTEM.

PRIVILEGES ARE GIVEN AND TAKEN BACK USING GRANT AND REVOKE COMMANDS

Privileges

SYSTEM ADMINISTRATOR has the authority on all objects in DB2. In order to perform any operation in DB2, the user must hold appropriate privilege for the operation and the object in question, Otherwise the request will be rejected. System administrator grants single or group (bundled) privileges to users.

Group of privileges (BUNDLED PRIVILEGES) used in DB2 are shown below

SYSADM

SYSTEM ADMINISTRATOR AUTHORITY allows the holder to execute any operation that the system supports.

SYSCTRL

SYSTEM CONTROL AUTHORITY allows the holder to execute any operation, except for operation that access database contents.Example: CREATE STOGROUP

DBADM

DATABASE ADMINISTRATOR AUTHORITY on a specific database allows the holder to execute any operation that the system supports on the database Example: SELECT, UPDATE etc

DBCTRL

DATABASE CONTROL AUTHORITY on a specific database allows the holder to execute any operation that system supports except for data manipulation operation Example: RECOVER DATABASE

DBMAINT

DATABASE MAINTENANCE AUTHORITY on a specific database allows the holder to execute read only maintenance functions on the databaseExample: DISPLAY DATABASE, START DATABASE etc

SYSOPR

SYSTEM OPERATOR AUTHORITY allows the holder to carry out console operator functions on the system.Example: STARTING AND STOPPING SYSTEM TRACE ACTIVITIES

PACKADM

package administrator authority on a specific collection allows the holder to create packages in that collection and gives the holder all package privileges in that collection

REFERENTIAL INTEGRITY

DB2’S REFERENTIAL INTEGRITY SUPPORT

THERE ARE TWO GENERAL INTEGRITY RULES IN DB2 FOR MAINTAINING DATA INTEGRITY

ENTITY INTEGRITY RULE

NO COMPONENT OF PRIMARY KEY OF A BASE TABLE IS ALLOWED TO ACCEPT NULLS.

REFERENTIAL INTEGRITY RULE

REFERENTIAL INTEGRITY RULE STATES THAT ALL NON NULL VALUES OF FOREIGN KEY MUST APPEAR AS A VALUE OF THE PRIMARY KEY OF SOME SPECIFIC TABLE

BY DEFINITION FOREIGN KEY IN ONE TABLE MATCHES A PRIMARY KEY.

A PRIMARY KEY MUST BE UNIQUE AND CANNOT BE NULL

A FOREIGN KEY VALUE MUST MATCH A PRIMARY KEY VALUE OR BE NULL

DB2’S Referential Integrity Support

Referential integrity consists of a set of rules used in DB2 to provide accuracy , validity or correctness of data in database. Maintaining integrity is of paramount importance and this task is handled by the system rather than the user . For this the system needs to be aware of integrity rules, it should monitor all operations and should ensure that they do not violate any of those rules.

DB2 supports ENTITY INTEGRITY RULE by enforcing the programmer to make the column declaration of the primary key not null. If the primary key is composite then all the columns in that composite key should be declared as not null. The justification for this is basically that the primary key values in base tables serve to identify entities in the real world. Primary keys are used for direct row level retrieval and relating one table to another in relational database. Therefore an unknown value in primary column will be meaningless.

DB2 enforces that values of a given foreign key must match the values of the corresponding primary key. But the converse is not a requirement. ie the primary key corresponding to some given foreign key might contain a value that currently does not appear as a value of that foreign key. Table which contains the primary key is the parent table and table containing foreign key is the dependent table.

This referential integrity rule can be violated during data manipulation like update, delete, insert. DB2 will monitor all operations and it will not allow any violation in referential integrity rules.

DB2 ENFORCEMENT OF REFERENTIAL INTEGRITY

DB2 ENFORCES REFERENTIAL CONSTRAINTS WHEN

AN INSERT STATEMENT IS APPLIED TO THE DEPENDENT TABLE

AN UPDATE STATEMENT IS APPLIED TO A FOREIGN KEY OF A DEPENDENT TABLE OR AN UPDATE OF THE PRIMARY KEY OF THE PARENT TABLE

A DELETE STATEMENT IS APPLIED TO A PARENT TABLE

AN INSERT INTO A PRIMARY KEY TABLE CANNOT VIOLATE REFERENTIAL INTEGRITY AND NO CHECKING IS REQUIRED

DELETION OF A FOREIGN KEY VALUE CANNOT VIOLATE REFERENTIAL INTEGRITY AND NO CHECKING IS REQUIRED

REFERENTIAL INTEGRITY ENFORCEMENT RULES

INSERT RULE

THE INSERTION OF ANY FOREIGN KEY VALUE IN THE DEPENDENT TABLE IS ALLOWED ONLY IF THE MATCHING VALUE EXISTS IN THE PRIMARY KEY OF THE PARENT TABLE

UPDATE RULE

CHANGES IN THE PRIMARY KEY VALUES ARE ALLOWED ONLY FOR THOSE VALUES THAT DO NOT HAVE MATCHING FOREIGN KEY VALUES

UPDATING A FOREIGN KEY VALUE IS ALLOWED ONLY IF SUCH A VALUE EXISTS IN THE PRIMARY KEY

DELETE RULE

DELETION OF A PRIMARY KEY VALUE WHEN A CORRESPONDING VALUE EXISTS

WILL BE BARRED IF THE FOREIGN KEY CONSTRAINT HAS

BEEN SPECIFIED AS RESTRICT WILL CAUSE DELETION OF THE CORRESPONDING FOREIGN

KEY VALUES IF THE CONSTRAINT HAS BEEN SPECIFIED AS

CASCADE WILL SET THE CORRESPONDING FOREIGN KEY VALUES TO

NULL IF THE CONSTRAINT HAS BEEN SPECIFIED SET NULL

Referential Integrity Enforcement Rules

When integrity constraints are in effect, a few data manipulations like INSERT, UPDATE, DELETE) hold the potential for integrity violations or for unpredictable or anomalous results. DB2 detects some of these situations when it attempts to bind SQL statements that result in problems. Instead of completing such a bind, DB2 issues an error message.

Insertion of rows containing new primary key values of the parent table do not require checks of associated foreign keys because additions pose no threat to referential integrity. Values added to foreign key columns of depended table through inserts, on the other hand must have corresponding primary key values.

Updating the primary key of the parent table will be restricted if matching foreign keys are found in dependent table. While updating the dependent table the new foreign key value must be present in the parent table. Otherwise the request will be rejected.

The delete rule of a referential constraint applies when a row of the parent table is deleted. The effect of this delete on dependent tables will dependent on the ON DELETE clause of FOREIGN KEY DEFINITION. The possible specifications of ON DELETE clause are RESTRICT, CASCADE, SET NULL.

When the deleting a primary key value, assume that the delete rule is RESTRICT, then the delete is restricted to the case where there are no matching rows in the dependent table. If matching rows exist then the delete request will be rejected.

The delete rule CASCADE deletes all matching rows. Ie This deletes the row corresponding to the primary key in parent table and the matching rows in dependent table.

For using the delete rule SET NULL the foreign key must have nulls allowed.Here row corresponding to the primary key value in the parent table will be deleted and the foreign key value will be set to null in all matching rows of the primary key in dependent table.

Example For Referential Integrity Violation

TABLE S TABLE SP


S1 SMITH 20 LONDON S1 P1 300 S2 JONES 10 PARIS S1 P2 200 S3 BLAKE 30 PARIS S1 P3 400 S4 CLARK 20 LONDON S1 P4 200 S5 ADAMS 30 ATHENS S1 P5 100

S1 P6 100 S2 P1 300 S2 P2 400 S3 P2 200 S4 P2 200 S4 P4 300 S4 P5 400

Consider tables S and SP for explaining the implications of REFERENTIAL INTEGRITY concept

PRIMARY KEY; FOREIGN KEY clauses of the create table statements for these tables are given below

TABLE SP TABLE S

PRIMARY KEY ( S#, p# ) PRIMARY KEY ( S# )FOREIGN KEY SFK ( S# )

REFERENCES SON DELETE CASCADE

FOREIGN KEY PFK ( P# )REFERENCES PON DELETE RESTRICT

In this example table S is the parent table and table SP is the dependent table. PFK and SFK are constraint names that will be used by DB2 in diagnostic messages relating to the foreign keys S# and P#. If the user does not specify the name DB2 will create one derived from the name of the first column participating in the foreign key.

Four different cases of potential referential integrity violations for these tables are explained below

CASE1An insert on the SP table might introduce a shipment for which there is no matching supplier. For example

INSERT INTO SP (S#, P#, QTY )VALUES ( ‘S20’, ……) ;

CASE2An update on column SP.S# of the SP table might introduce a shipment supplier number for which there is no matching supplier. For example

UPDATE SPSET S# = ‘S20’WHERE….;

CASE3A deletion on the S table might remove a supplier for which there exists a matching shipment. For example

DELETE FROM SWHERE S# = ‘S1’ ;

CASE4An update on column S.S# of the S table might remove a supplier for which there exists a matching shipment . For example

UPDATE SSET S# = ‘S20’WHERE S# = ‘S1’ ;

In order to enforce referential constraint, the system must deal with all four of these cases.

Explanation

CASE1This situation is prevented by the virtue of the fact that SP.S# is a foreign key in table SP matching the primary key S.S# of table S. Such an insert will simply be rejected. But an insert that introduces a shipment for a supplier that does already exist in table S will be accepted.

CASE2In this case also the update will be rejected . But an update that introduces an SP.S# value that does already exist in table S will be accepted.

CASE3This situation is handled by the delete rule CASCADE. In general RESTRICT would mean that the delete will be accepted only if there no such matching shipments. CASCADE would mean that any such matching shipments will de removed anyway. And SET NULL would mean that any such matching shipments will not be removed but will be updated so that they are no longer matching.

CASE4

This situation is handled by the implicit update rule restrict, which means that the update will be accepted only If no such matching shipments exist.

DATABASE RECOVERY IN CASE OF FAILURE

UNIT OF RECOVERY

POINT OF NEW POINT OFCONSISTENCY CONSISTENCY

OLD DATA UPDATES UPDATED

DATA UNIT OF RECOVERY DATA

COMMIT

POINT OF NEW POINT OFCONSISTENCY CONSISTENCY

ABNORMALTERMINATION

DATA UPDATES BACK OUT UPDATESOLD OLD

DATA DATA

SUCCESSFUL EXECUTION OF MULTIPLE SQL STATEMENTS MAY BE NECESSARY TO COMPLETE A LOGICAL UNIT OF RECOVERY

THE APPLICATION PROGRAMMER MUST DETERMINE THE LOGICAL UNIT OF RECOVERY

DATABASE RECOVERY IS DONE TO THE LAST POINT OF CONSISTENCY

Unit Of Recovery

A unit of recovery is the work done by a DB2 for an application, that changes DB2 data from one point of consistency to another. A point of consistency is a time when all recoverable data that an application program accesses is consistent with other data.

A unit of recovery begins with the first change to the data after the beginning of the job or following the last point of consistency and ends at a later point of consistency. If failure occurs within a unit of recovery, DB2 backs out any changes to data, returning the data to its state at the start of the unit of recovery; that is, DB2 undoes the work.

DATA RECOVERY

BACKUP

DATA BASE UPDATEDDATABASE

FCOMMIT A

ILU

UPDATE1 UPDATE2 RE

LOG

BACKUP

RECOVEREDDATABASE

RESTORE

UPDATE

LOG

Data Recovery

Backups are maintained by database administration for the data in DB2 subsystem. Backups may be of the entire database or of one or more tablespaces. In case of failure database recovery is done using these backups.

All data changes and other significant activities are recorded in logs by DB2. Database manager may use the backup copies and the logs to re-establish the data base to the last committed unit of work. Changes that were not committed before the failure are not recovered in any case

In the given example, the backup is made for a database by DB2. After that the database is changed , and that is made permanent by issuing a commit. Again the application program tries to do another update and before it’s completion a failure occurs

Now we want to recover the data in the database. The database is recovered from he backup and the changes that were made in that database till the last commit were done. and the database is restored.

9. Concurrency

Objects in DB2 can be used by many users at the same time. This is achieved by the using proper locking system. This chapter explains how DB2 uses these locks and how much control the programmer has over the concurrency in DB2.

9.1. Concurrency

9.2. Locking Strategy

9.3. Lock Sizes And Types

9.4. Acquire Release Parameters

9.5. Isolation Parameter

CONCURRENCY

DB2 ALLOWS ANY NUMBER OF USERS TO ACCESS THE SAME TABLE AT THE SAME TIME .THIS IS CALLED CONCURRENCY

DB2 USES A CONCURRENCY CONTROL MECHANISM TO AVOID ERRORS AND INCONSISTENCIES IN DATA WHEN MULTIPLE USERS ACCESS THE SAME DATABASE.

DB2 MANAGES CONCURRENCY CONTROL WITH SEVERAL TYPES OF LOCKS THAT RESTRICT ACCESS TO DATA WHILE THEY ARE BEING USED

CONCURRENCY CONTROL ELIMINATES THE POSSIBILITY OF ONE USER CHANGING DATA WHILE ANOTHER IS IN THE PROCESS OF USING OR CHANGING THEM WHICH CAN LEAD TO ERRORS OR INCONSISTENCIES IN DATA.

Concurrency

DB2 is a shared system, that is a system that allows any number of users to access the same database at the same time. Any such system requires some kind of concurrency control mechanism to ensure that concurrent transactions do not interfere with each other operation. The absence of such a mechanism will lead to errors and inconsistencies in data

DB2 uses locks to control access to same database by multiple users. The basic idea of locking is simple, when a transaction needs an assurance that some object that is interested in, will not change in some unpredictable manner by another user. An exclusive lock on the object will provide this assurance. The effect of the lock is to lock other transactions out of the object, and thereby to prevent them from changing it. The first transaction is thus able to carry out its processing in the certain knowledge that the object in question will remain in a stable state for as long as the transaction wishes to.

If a transaction requests a lock that is not currently available, then the transaction simply waits until it gets it. In practice the installation can specify a maximum wait time; If a transaction ever reaches that threshold in waiting for a lock, it times out and the lock request is failed.

LOCKING STRATEGY

DB2 DETERMINES IT’S LOCKING STRATEGY FOR EACH PROGRAM WHEN IT BINDS THE APPLICATION PLAN. THE LOCKING STRATEGY DEPENDS ON SEVERAL FACTORS

THE LOCK SIZES DECLARED IN THE LOCKSIZE PARAMETER OF CREATE TABLESPACE STATEMENT

TYPE OF SQL STATEMENTS

THE PRESENCE OF EXPLICIT LOCK TABLE STATEMENTS

THE ACQUIRE AND RELEASE OPTIONS CHOSEN BY THE DEVELOPER AT BIND TIME

THE ISOLATION LEVEL CHOSEN AT BIND TIME.

THE ACCESS PATH CHOSEN

Locking Strategy

DB2 allows multiple users to access same object at same time, but they are controlled by locks. DB2 selects appropriate locking mechanism based on concurrency control requirements inherent in the application program. They are called implicit locks.

In addition to the implicit locking mechanism, DB2 provides certain explicit facilities.

These explicit facilities are

1. LOCKSIZE parameter of CREATE TABLESPACE statement.2. ISOLATION parameter3. ACQUIRE / RELEASE parameter4. SQL statement LOCKTABLE.

Lock table statement can be coded in the application program to acquire an explicit lock on an object on behalf of the application program. Other parameters are explained in the following pages.

Example

LOCK TABLE SP IN EXCLUSIVE MODE;

LOCK SIZES AND TYPES

THE SIZE (SCOPE) OF A LOCK ON DATA IN A TABLE DESCRIBES THE AMOUNT OF DATA CONTROLLED

THE SIZE IS SPECIFIED IN THE LOCKSIZE PARAMETER OF CREATE TABLESPACE STATEMENT

LOCKSIZE TABLESPACETHIS MEANS THAT ALL LOCKS ACQUIRED ON DATA IN THE TABLE SPACE WILL BE AT THE TABLE SPACE LEVEL

LOCK SIZE TABLETHIS MEANS THAT LOCKS ACQUIRED ON DATA IN THE TABLE SPACE WILL BE AT THE TABLE LEVEL

LOCKSIZE PAGETHIS MEANS THAT LOCKS ACQUIRED ON DATA IN THE TABLE SPACE WILL BE AT TABLE LEVEL

LOCKSIZE ROWTHIS MEANS THAT THE LOCKS ACQUIRED ON DATA IN THE TABLE SPACE WILL BE AT THE ROW LEVEL

LOCKSIZE ANYTHIS MEANS THAT DB2 WILL DECIDE THE APPROPRIATE PHYSICAL UNIT OF LOCKING FOR THE TABLESPACE

DB2 ALWAYS REQUIRES A TABLE OR TABLESPACE LOCK BEFORE ACCESS TO DATA IS PERMITTED .

DB2 MAY USE TABLE OR TABLESPACE LOCK ALONE TO ACCESS DATA ACCORDING TO THE LOCKSIZE PARAMETER

IF THE LOCKING STRATEGY INCLUDES ROW OR PAGE LOCKING THEN DB2 LOCKS TABLE OR TABLE SPACE BEFORE LOCKING ROW OR PAGE

Lock Sizes And Types

Proper selection of lock size is important for better performance and concurrency of the database. A locksize of tablespace allows a process to lock the tablespace which controls all tables inside the table space. On the other hand row lock will only lock the row which the application program wants.

In a simple tablespace locking table space means locking all tables inside that table space which will reduce concurrency. But a page lock will lock only those rows of tables present in that page and other users can access other rows in that tablespace concurrently.

Locking larger or smaller amounts of data allows you to trade performance for concurrency. When you use page or row locks instead of table or tablespace locks concurrency usually improves, meaning better response times .When you use only table or tablespace locks then processing time and storage used is reduced. But concurrency is also reduced , meaning longer response times for some users.

For maximum concurrency, locks on a small amount of data held for a short duration are better than locks on a large amount of data held for a long duration of time. However acquiring a lock requires processor time, and holding a lock requires storage. These things should be kept in mind while deciding a lock size.

ACQUIRE RELEASE PARAMETERS

ACQUIRE AND RELEASE ARE BIND OPTIONS WHICH WILL DETERMINE WHEN TO ACQUIRE AND RELEASE ITS LOCKS

ACQUIRE ( ALLOCATE )ACQUIRES THE LOCK WHEN THE PLAN IS ALLOCATED

ACQUIRE (USE )ACQUIRES THE LOCK WHEN THE OBJECT IS FIRST ACCESSED.

RELEASE (DEALLOCATE)RELEASES THE LOCKS WHEN THE PLAN IS DE ALLOCATED

RELEASE(COMMIT)RELEASES THE LOCK AT THE NEXT COMMIT POINT. IF THE APPLICATION ACCESSES THE OBJECT AGAIN IT MUST ACQUIRE THE LOCK AGAIN

ISOLATION PARAMETER

ISOLATION PARAMETER SPECIFIES THE LOCKING STRATEGY FOR CURSORS

THE ISOLATION LEVEL CHOSEN FOR AN APPLICATION CAN IMPACT BOTH THE LOCK STRATEGY AND THE DURATION OF ROW LOCKS

THE ISOLATION LEVEL CAN BE SPECIFIED DURING BIND TIME

DIFFERENT ISOLATION LEVELS ARE

REPEATABLE READ(RR) READ STABILITY(RS) CURSOR STABILITY(CS) UNCOMMITTED READ(UR)

DEFAULT VALUE FOR ISOLATION PARAMETER IS REPEATABLE READ(RR)

ISOLATION SPECIFIES THE DEGREE TO WHICH OPERATIONS ARE ISOLATED FROM THE POSSIBLE EFFECTS OF OTHER OPERATIONS ACTING CONCURRENTLY.

BASED ON THIS INFORMATION, DB2 CHOOSES TABLE AND TABLE SPACE LOCKS AS NONRESTRICTIVE AS POSSIBLE, AND RELEASES S AND U LOCKS ON ROWS OR PAGES AS SOON AS POSSIBLE.

Isolation parameter

If an SQL statement embedded in a host language program will return multiple rows, the developer must declare in the program a cursor that presents them to the host program one at a time, usually with in a repeatedly executed block. DB2 can handle locking for these cursors using different ISOLATION levels.

ISOLATION(RR) Repeatable read: A row or page lock is held for all accessed rows, qualifying or not, at least until the next commit point. If the application process returns to the same page and reads the same row again, the data cannot have changed and no new rows can have been inserted.

ISOLATION (RS) Read stability: A row or page lock is held for pages or rows that are returned to an application at least until the next commit point. If a row or page is rejected during stage 2 processing, its lock is still held, even though it is not returned to the application.

If the application process returns to the same page and reads the same row again, the data cannot have changed, although additional rows might have been inserted by another application process. A similar situation can also occur if a row or page that is not returned to the application is updated by another application process. If the row now satisfies the search condition, it appears.

ISOLATION(CS) Cursor stability: A row or page lock is held only long enough to allow the cursor to move to another row or page. For data that satisfies the search condition of the application, the lock is held until the application locks the next row or page. For data that does not satisfy the search condition the lock is immediately released.

ISOLATION(UR) Uncommitted read: The application acquires few locks and can run concurrently with most other operations. But the application is in danger of reading data that was changed by another operation but not yet committed.

10. DB2I (DB2 Interactive )

DB2I is an interactive facility available in DB2 . Almost all of the functions of DB2 are available in DB2I , Which can be used by developers .This chapter contains

10.1. DB2I

10.2. SPUFI

DB2I (DB2 INTERACTIVE )

THE DB2 INTERACTIVE INTERFACE IS A TSO ONLINE APPLICATION WHICH WORKS UNDER THE CONTROL OF ISPF(INTERACTIVE SYSTEM PRODUCTIVITY FACILITY) WHICH IS A SCREEN /DIALOG MANAGER FOR TSO

DB2I PROVIDES OPTIONS FOR ALL THE DB2 FUNCTIONS THAT DEVELOPERS ARE LIKELY TO NEED

DB2 FUNCTIONS THAT ARE AVAILABLE THROUGH DB2I ARE SHOWN IN THE DB2PRIMARY OPTION MENU

DB2 PRIMARY OPTION MENU

= = = >

select one of the following db2 functions and press enter

1 SPUFI (Process SQL statements)2 DCLGEN (Generate SQL and sorce language

declarations)3 PROGRAM PREPARATION (Prepare a DB2 application program

to run)4 PRE COMPILE (Invoke DB2 pre compiler)5 BIND/REBIND/FREE (Bind rebind or free appl. Plans or

packages) 6 RUN (RUN an SQL program)7 DB2 COMMANDS (Issue DB2 commands)8 UTILITIES (Invoke DB2 utilities)9 CATALOG VISIBILITY (Invoke catalog dialogs)d DB2I DEFAULTS (set global parameters) x EXIT ( leave DB2)

DB2I

DB2 provides a number of commands for use in readying a program for execution that programmers can use to perform the functions required to convert code from source to executable modules. A convenient alternative is to work through DB2I , which provides a menu interface to the necessary command processor . If you develop programs using TSO and ISPF, you can prepare them to run using the DB2 Program Preparation panels. These panels guide you step by step through the process of preparing your application to run. There are other ways to prepare a program to run, but using DB2I is the easiest, as it leads you automatically from task to task.

DB2I primary option menu lists the functions it can perform. The user can select any one of these functions according to his requirements

SPUFI (SQL processor using file input) supports the online execution SQL statements from a TSO terminal. SPUFI is intended basically for application programmers who wish to perform SQL portions of their programs.

The DCLGEN menu allows users to invoke the declarations generator program, which produces the DECLARE TABLE statements and host language data structure.

Other options like PRECOMPILE, BIND, RUN are used for preparing and executing DB2 application program.

UTILITIES menu helps the user to invoke DB2 online utilities like LOAD, REORG, RECOVER etc. The necessary utility control statements to direct the operation of the specific utility must be created before the utility is invoked.

SPUFI

INPUT SQL SPUFI OUTPUTSTATEMENTS RESULTS

DB2

SPUFI PROCESSES INCLUDE

PREPARING INPUT FILE FOR SPUFI

DB2I SUBMITS THE SQL TO DB2

SUCCESSFUL JOBS ARE AUTOMATICALLY COMMITTED

EXAMINING THE RESULTS OF SQL

11. Utilities

For analyzing and managing physical data present in data base, DB2 offers a number of utilities . This chapter gives a brief explanation of these utilities

11.1. Load

11.2. Runstats

11.3. Reorg

UTILITIES

DB2 OFFERS A NUMBER OF UTILITIES FOR ANALYZING

AND MANAGING THE PHYSICAL STORAGE OF DATA .

THERE ARE TWO TYPES OF DB2 UTILITIES.

ONLINE UTILITIES STAND ALONE UTILITIES

DB2 ONLINE UTILITIES RUN AS STANDARD MVS BATCH JOBS, AND THEY REQUIRE DB2 TO BE RUNNING

THE STAND-ALONE UTILITIES EXECUTE AS BATCH JOBSINDEPENDENT OF DB2. THEY CAN BE INVOKED ONLY BY MEANS OF MVS JCL.

IMPORTANT ONLINE UTILITIES ARE

LOAD REORG RECOVER RUNSTATS

IMPORTANT STAND ALONE UTILITIES ARE

DSNJU003 DSNJU004 DSN1CHKR

LOAD

THE LOAD UTILITY LOADS DATA FROM A SEQUENTIAL FILE TO ONE OR MORE TABLES IN A TABLESPACE

INPUT LOAD UTILITY CORRECT DATA DB2 TABLE DATA

EXAMPLE

CONTROL INFORMATION FOR LOAD UTILITY

LOAD DATA RESUME NOLOG NOinddn ddnameINTO TABLE D2110K.S( S# POSITION (1) CHAR 5P# POSITION (6:11) CHAR 6QTY POSITION (12:15) INTEGER );

Load

Load utility is used to load data from a sequential file to a TABLE in a table space.In the previous example the TABLE S is loaded from the dataset specified in the load jcl. ddname of the input dataset that is used in the LOAD JCL is given in INDDN parameter. Each fields and their positions are also specified.

If the table space already contains data, you can choose whether you want to add new data to existing data or replace the existing data. This can be done using the parameter RESUME.

There are three options for RESUME.

RESUME NO: Indicates that the dataset is to be empty. This is the default option.

RESUME NO REPLACE: This causes the utility to over write the existing data.

RESUME YES: This allows the utility to add new rows to the existing table.

The LOG NO command instructs the utility not to record data in the log as they are loaded .IF the user does not specify LOG NO , the utility records the changes which can be used for recovery purpose. Default is LOG YES. Recording data in the log during a load can increase the time required for the load significantly.

RUNSTATS

RUNSTATS UTILITY COLLECTS STATISTICS OF TABLESPACEAND UPDATES CATALOG TABLES

RUNSTATS SHOULD BE EXECUTED IMMEDIATELY AFTER A TABLE AND IT’S INDEXES ARE CREATED AND THE DATA IS LOADED

DB2 OPTIMIZER CAN TAKE ADVANTAGE OF THESE UPDATEDCATALOG TABLES TO SELECT BEST ACCESS STRATEGY

EXAMPLE

CONTROL INFORMATION FOR RUNSTATS UTILITY

RUNSTATS TABLESPACE D2110K.TABSPTABLE(ALL)INDEX(ALL) ;

Runstats

The RUNSTATS utility reads tablespaces and indexes to collect statistics describing the data. The main statistics collected include number of rows in the table, number of pages that contain the rows of the table, number of distinct values of indexed column , percentage of space occupied by rows etc. RUNSTATS utility uses this information to update CATALOG tables.

In the previous example RUNSTATS utility is used for table space TABSP in database D2110K. All tables in the tablespace are specified by TABLE(ALL) keyword. Here you can specify the table name in parentheses after keyword TABLE on which the utility has to run. You can obtain statistics on all indexes on all tables in the named table space by specifying INDEX(ALL).The user can get statistics of one more specific indexes by specifying them in parentheses after the keyword INDEX .

The RUNSTATS utility is useful for finding out the free space remaining in a tablespace and we use that information for reorganizing the tablespace.

REORG

REORG UTILITY IS USED TO REORGANIZES DATA ONPHYSICAL STORAGE OF TABLES. DIFFERENT PHASESOF REORG UTILITY ARE

UNLOADS ROWS FROM A TABLE SPACE RELOADS ROWS IN A NEATER ARRANGEMENT

WITH FREE SPACE REBUILDS INDEXES DOES NOT VALIDATE DATA

CONTROL STATEMENTS FOR REORG UTILITY

REORG TABLESPACE D2110K.TABSPLOG NO;

Reorg

The REORG online utility reorganizes a table space or index to improve access performance and reclaim fragmented space. In addition, the utility can reorganize a single partition of either a partitioned index or a partitioned table space.

REORG utility reorganizes table space or index as you specify in control statements. When an index space only is reorganized then the data pages are not processed. Only leaf pages which contains indexes are scanned.

Proper scheduling of reorganizations significantly improves performance of all application programs.

In the given example REORG utility is run on tablespace TABSP in database D2110K. If you want to reorganize an index then specify REORG INDEX (index name) . LOG NO parameter is specified in the example to avoid writing data records in the log while loading the tablespace.

12. Advanced DB2

This section explains some of the advanced concepts in DB2. The detailed discussions on indexes and DB2 locks are included. Advanced topics present in this section are

12.1. More About Indexes

12.1.1. Example Of An Index

12.1.2. Clustered Indexes

12.1.3. Non Clustered Indexes

12.2. Special Registers

12.3. More About Locks

12.3.1. Modes Of Table And Tablespace Locks

12.3.2. Modes Of Row And Page Locking

12.3.3. Lock Mode Compatibility Of Table And Table Space Locks

12.3.4. Lockmode Compatibility Of Row And Page Locks

12.4. Invoking Online Utilities

More About Indexes

DB2 uses indexes not only to enforce uniqueness on column values, as for primary keys, but also to cluster data, partition tables, and to provide access paths to data for queries. Understanding some of the structure of DB2 indexes can be important for achieving your best performance.

A table can have more than one index, and an index key can use one or more columns. An index key is a column or an ordered collection of columns on which an index is defined. A composite key is a key built on 2 to 64 columns.

The usefulness of an index depends on its key. Columns that you use frequently in performing selection, join, grouping, and ordering operations are good candidates for use as keys

DB2 allows you to enter duplicate values in a key column. If you do not want duplicate values, use CREATE UNIQUE INDEX. If a table has a primary key, its entries should be unique. Its uniqueness is enforced by defining a unique index on the primary key columns,

EXAMPLE OF AN INDEX

25 61 86 ROOT PAGE

8 17 25 33 40 61 70 75 86 INTER- MEDIATE PAGES

LEAF PAGES

. . 8 . . 17 . . 25 . . 33 . 40 . . 61 . . 70 . . 75 . . 86

POINTERS TO DATA RECORDS

DATAPAGES

THE INDEX IS STRUCTURED AS A B-TREE

A RECORD IS LOCATED USING ROOT PAGE, INTERMEDIATE PAGES AND LEAF PAGES

THE PAGE SIZE OF AN INDEX IS 4KB

Example Of An Index

Indexes in DB2 are based on a structure known as B-Tree. Indexes can have more than one level of pages. Index pages that point directly to the data in the tables are called leaf pages. If the index has more than one leaf page, it must have at least one non leaf page, containing entries that point to leaf pages. If it has more than one non leaf page, the non leaf pages whose entries point directly to leaf pages are said to be on the first level; there must be a second level of non leaf pages to point to the first, and so on. The highest level contains a single page, called the root page.

A typical index is shown in the figure, which is a multilevel, tree structured index with the property that the tree is always balanced, that is that is all leaf entries in the structure are equidistant from the root of the tree. and this property is maintained as new entries are inserted into the tree and existing entries are deleted

The root page is the top of the structure. The root page will contain an entry for each non leaf or immediate page. The entry in the root page consists of the high value contained on the intermediate page and a pointer to that page.

The immediate pages are similar in structure to the root page, expect that the range of values addressed is more specific. The immediate page contains an entry for each of the leaf pages addressed. The entry consists of the high value contained on the leaf page and a pointer to this leaf page.

The leaf pages contain the RID, using which the record can be located in a table space. The leaf pages collectively address the entire table.

CLUSTERED INDEXES

25 61 ROOT PAGE

8 17 33 40 INTERMEDIATEPAGES

LEAFPAGES

DATAPAGES

A CLUSTERING INDEX IS ONE IN WHICH THE RECORDS ARE PHYSICALLY STORED IN DATA PAGES IN THE SEQUENTIAL ORDER OF THEIR INDEX VALUES

HIGH PERFORMANCE BECAUSE OF REDUCED I/O OPERATIONS

EACH TABLE CAN HAVE ONLY ONE CLUSTERING INDEX

CLUSTERING INDEXES ARE EXTREMELY IMPORTANT FOR OPTIMIZATION PURPOSES. OPTIMIZER WILL TRY TO CHOOSE AN ACCESS PATH BASED ON THE CLUSTERING INDEX

Clustered Index

A clustering index is one for which the sequence defined by the index is the same as or close to the physical sequence. The clustering holds the most potential for performance gains. With a clustering index DB2 takes responsibility for maintaining rows in sequence on the clustering index columns as long as there is free space. DB2 maintains clustering by placing inserted rows in the indexed column’s sequence on available free space in the data pages.DB2 can then process the table in that order efficiently. If it is a non clustering index then DB2 has to reread data pages to identify all the qualifying rows, which will reduce performance.

Clustering is valuable when DB2 must process a column’s values in sequence. The SQL statements ORDER BY, GROUP BY, and DISTINCT require such processing. If a column specified in these operation and there is not a suitable index on the column, DB2 must sort it to put it in sequence before returning even one row to the user. If there is a clustering index on that column DB2 uses this column to retrieve the rows in sequence and return the rows immediately one by one.

To specify a clustering index, use the CLUSTER clause in the CREATE INDEX statement.

CREATE INDEX STATEMENT FOR A CLUSTERED INDEX

CREATE UNIQUE INDEX D2110N.I11010U1ON D2110N.T11010(TAB_INDEX)BUFFERPOOL BP0USING STOGROUP SGDB2OPCTFREE 20FREEPAGE 10PRIQTY 40SECQTY 20CLOSE NOCLUSTER;

NON CLUSTERED INDEXES

25 61 ROOT PAGE

8 17 33 40 INTERMEDIATEPAGES

LEAFPAGES

DATAPAGES

IN A NON CLUSTERED INDEX THE DATA ROWS DO NOT CORRESPOND TO THE ORDER OF THE INDEX ENTRIES

SPECIAL REGISTERS

A SPECIAL REGISTER IS A STORAGE AREA THAT DB2 DEFINES FOR A PROCESS

SPECIAL REGISTERS USED IN DB2 ARE

CURRENT DATE CURRENT DEGREE CURRENT PACKAGESET CURRENT RULES CURRENT SERVER CURRENT SQLID CURRENT TIME CURRENT TIMESTAMP CURRENT TIMEZONE USER

Special Registers

DB2 supports a number of special registers. A special register is a storage area that DB2 defines for a process. Wherever its name appears in an SQL statement, the name is replaced by the register's value when the statement is executed. Thus, the name acts like a function that has no arguments. (zero argument built in scalar functions)

You can use the SET statement to change the current value of a register. Where the register's name appears in other SQL statements, the current value of the register replaces the name when the statement executes. A commit or rollback operation has no effect on the values of special registers. Nor does any SQL statement, other than SET statement can change a register value

CURRENT DATE, specifies the current date. The data type is DATE. The date is derived by the DB2 that executes the SQL statement that refers to the special register.

Example: Display the average age of employees.

SELECT AVG(YEAR(CURRENT DATE - BIRTHDATE)) FROM DSN8410.EMP;

CURRENT PACKAGESET specifies a string of blanks or the collection ID of the package or packages that will be used to execute SQL statements. The data type is CHAR(18).

EXAMPLE Example: For executing a program, identify the collection ID for its package as EWSA.

SET CURRENT PACKAGESET = 'EWSA';

CURRENT SQLID specifies the SQL authorization ID of the process. The data type is CHAR(8). This SET statement is used to change the authorization id for a process

Example: Set the SQL authorization ID to 'GROUP34' (one of the authorization IDs of the process).

SET CURRENT SQLID = 'GROUP34';

CURRENT TIME, specifies the current time. The time is derived by the DB2 that executes the SQL statement that refers to the special register. ,

Example: Display information about all project activities and include the current date and time in each row of the result.

SELECT DSN8410.PROJACT.*, CURRENT DATE, CURRENT TIMEFROM DSN8410.PROJACT;

CURRENT TIMESTAMP, specifies the current timestamp. The data type is TIMESTAMP. The timestamp is derived by the DB2 that executes the SQL statement that refers to the special register.Example: Display information about the full image copies that were taken in the last week.

SELECT * FROM SYSIBM.SYSCOPYWHERE TIMESTAMP > CURRENT TIMESTAMP - 7 DAYS;

CURRENT USER specifies the primary authorization ID of the process. The data type is CHAR(8).

Example: Display information about tables, views, and aliases that are owned by the primary authorization ID of the process.

SELECT * FROM SYSIBM.SYSTABLES WHERE CREATOR = USER;

MORE ABOUT LOCKS

MODES OF TABLE AND TABLESPACE LOCKS

IS INTENT SHARE

IX INTENT EXCLUSIVE

S SHARE

U UPDATE

SIX SHARE WITH INTENT EXCLUSIVE

X EXCLUSIVE

IS : THE LOCK OWNER CAN READ ANY DATA IN THE TABLE IF AN S

LOCK CAN BE OBTAINED ON THE TARGET ROW OR PAGE

IX : THE LOCK OWNER CAN READ OR CHANGE ANY DATA IN THETABLE PROVIDED AN X LOCK CAN BE OBTAINED ON ROWS OR PAGES TO BE CHANGED AND A U OR S LOCK CAN BE OBTAINED ON ROWS TO BE READ

SIX: THE LOCK OWNER CAN READ ANY DATA IN THE TABLE AND CHANGE ROWS IN THE TABLE PROVIDED IT CAN OBTAIN AN X LOCK ON THE TARGET ROW OR PAGE FOR CHANGE. ROW LOCKS ARE NOT OBTAINED FOR READING.

S : THE LOCK OWNER CAN READ ANY DATA IN THE TABLE AND WILL NOT OBTAIN ROW OR TABLE LOCKS

U : THE LOCK OWNER CAN READ ANY DATA IN THE TABLE AND MAY CHANGE DATA IF AN X LOCK ON THE TABLE CAN BEOBTAINED. NO ROW OR PAGE LOCKS ARE OBTAINED

X : THE LOCK OWNER CAN READ OR UPDATE ANY DATA IN THE TABLE. ROW LOCKS ARE NOT OBTAINED

Modes Of Table And Tablespace Locks

The locking modes IS IX SIX are used at the TABLE OR TABLESPACE level to support row or page locks. They permit row or page level locking while preventing more exclusive locks on the table by other applications.

When an application obtains an IS lock on a table, that application may acquire a lock on a row or page for read only. Other applications can also read the same row. In addition other applications can change data on other rows in the table.

An application having an IX lock on a table can change a row after acquiring a row or page lock. Other applications can READ/CHANGE data on other rows in the table.

When an application has an SIX lock on a table, that application may acquire a lock on a row for change. Other application can only read other rows in the table.

The modes S U and X are used at the table level to enforce the strict table locking strategy. No row or page level locking is used by application that possess one of these locking modes.

When an application obtains an S lock on a table, that application can read any data in that table. It will allow other applications to obtain locks that support read only requests for any data in the entire table. No application can change any data in the table until s lock is released.

When an application obtains a U lock on a table , that application can read any data from that table and may eventually change data in that table by obtaining an X lock. Other applications can only read data In that table.

When an application obtains an X lock on a table that application can read and change any or all data in the table or tablespace . No other application can access data in the entire table or tablespace for READ or CHANGE

MODES OF ROW AND PAGE LOCKING

ROW/PAGE LOCK MINIMUM SUPPORTINGTABLE/TABLE SPACE LOCK

S SHARE IS

U UPDATE IX

X EXCLUSIVE IX

S : THE ROW IS BEING READ BY ONLY ONE APPLICATION AND IS AVAILABLE FOR READ ONLY BY OTHER APPLICATIONS

U : THE ROW IS BEING READ BY ONE APPLICATION BUT IS

POSSIBLY TO BE CHANGED BY THAT APPLICATION. THE ROW IS AVAILABLE FOR READ ONLY BY OTHER APPLICATIONS

X : THE ROW IS BEING CHANGED BY ONE APPLICATION AND ISNOT AVAILABLE FOR OTHER APPLICATION

ROW LEVEL LOCKS ARE ONLY REQUESTED BY APPLICATIONS THAT HAVE SUPPORTING LOCKS AT THE TABLE LEVEL

LOCK MODE COMPATIBILITY OF TABLE AND TABLE SPACE LOCKS

MODE OF MODE OF LOCK B LOCK A

IS S IX SIX U X

IS YES YES YES YES YES NO

S YES YES NO NO YES NO

IX YES NO YES NO NO NO

SIX YES NO NO NO NO NO

U YES YES NO NO NO NO

X NO NO NO NO NO NO

THE SYMBOLS A AND B IN THE ABOVE DIAGRAM ARE USED TO REPRESENT TWO DIFFERENT APPLICATIONS

THIS CHART IS USEFUL TO DETERMINE IF TWO APPLICATION CAN RUN CONCURRENTLY IF THEY ARE ACCESSING SAME TABLE WITH THE GIVEN LOCK MODE AT THE SAME TIME.

Lock Mode Compatibility Of Table And Table Space Locks

If application A obtains an IS lock against a given table application B could obtain an IS, S, IX, SIX or U lock against the same table at the same time. However an X lock would not be permitted at the same time.

This particular example illustrates the concept of IS lock acting as supporting lock for a lower level of locking. The only table lock that is not compatible is X lock which would require exclusive lock use of the table. The presence of IS lock indicates that a lower level of locking is required for this table and X lock is not given.

Study of the chart reinforces the definitions of table and row lock modes presented on previous pages. Review the row for IX under application A. Assume that application A obtains an IX lock on table Y. This lock indicates that the application intends to obtain locks to support change at the row level. The application will allow other rows to be read and updated but will prevent access to the target rows Examine each of the possible competing table locks that application B might request

IS-- Intent to lock for read only at row level. This lock is compatible. There may be contention at the row level if application A is changing the same row that application B wants to read.

S-- Share lock at the table level. This lock is not compatible since the S lock states that the entire table is available for read only by the application possessing the lock and all other applications. The IX lock states that an intent to change data at the row level which contradicts the requirement for read only. Therefore application B could not obtain the S lock

IX-- Intent to lock for change at the row level. This lock is compatible. There may be lock contention at the row level if application A is changing the same row that application B wants to change.

SIX—The SIX lock states that lock request for changing data may be required at the row level for the application processing the lock. In addition the rest of the table is available for read only applications. The IX lock implies change at the row level as well. Application B could obtain six lock on the table

U-- Read with intent to update. This table level lock states that the application processing the lock may read any data and may potentially exchange the U lock for an X lock. However until this exchange is done other applications can obtain locks supporting read only. Application B would not be able to obtain the U lock at the same time that application a possessed an IX lock on the same table.

X-- The application possessing this mode of lock on the table requires exclusive use of the table. No other access is permitted. The ix lock possessed by an application A would prevent application B from obtaining x lock

The same type of statements can be logically derived for the other rows in the chart

LOCK MODE COMPATIBILITY OF ROW AND PAGE LOCKS

MODE MODE OF LOCK B OF LOCK A S U X

S YES YES NO

U YES NO NO

X NO NO NO

THIS CHART IS USEFUL TO DETERMINE IF TWO APPLICATION CAN RUN CONCURRENTLY IF THEY ARE ACCESSING SAME ROW WITH THE GIVEN LOCK MODE AT THE SAME TIME.

CONSIDER AN APPLICATION A HAVING AN S LOCK ON ROW Y. THEN ANOTHER APPLICATION B CAN ONLY GET LOCKS AND U ON THAT ROW

IF AN APPLICATION A HAS A SHARE LOCK ON A ROW IT, WILL ALLOW OTHER APPLICATIONS TO READ THE SAME ROW. SO APPLICATION B CAN GET AN S LOCK ON THE SAME ROW AT THE SAME TIME

AN APPLICATION B CAN GET AN UPDATE LOCK ON A ROW WHICH IS CURRENTLY LOCKED BY AN S LOCK OF APPLICATION A. IF THE APPLICATION B WANTS TO CHANGE THAT ROW DB2 WILL WAIT UNTIL THE S LOCK IS REMOVED AND IT WILL PROMOTE THE U LOCK TO AN X LOCK.

NO TWO APPLICATION CAN HAVE AN EXCLUSIVE LOCK ON THE SAME ROW AT THE SAME TIME

THE SAME TYPE OF STATEMENTS CAN BE LOGICALLY DERIVED FROM OTHER ROWS OF ABOVE CHART.

Invoking Online Utilities

Creating utility control statements is the first step required to run an online utility. Utility control statements define the function the utility job performs. Utility control statements are read from the SYSIN input stream. The SYSIN stream can contain multiple utility control statements. Control statements are different for each utility and are explained in chapter 11

There are different methods of invoking DB2 online utilities. Commonly used methods are using DB2I and IBM supplied JCL procedure DSNUPROC.

When you use DB2I (DB2 interactive ) panel for executing a utility you must specify the name of the utility , the dataset which contains the control information and other datasets needed by the the utility. Then you can execute the utility from that panel.

DB2 on line utilities can be invoked using DSNUPROC procedure, For that you must write and submit JCL, in your JCL, the EXEC statement invokes the DSNUPROC procedure. You must give the control statements as input to DSNUPROC and use the necessary datasets required for the execution of the utility.

Sample JCL For Invoking Online Utilities

/EX6216X JOB SW301709,'I65000 XT01DL1', // NOTIFY=&SYSUID, // MSGCLASS=8,REGION=6M, // TIME=15,LINES=200 //* //PROCLIB JCLLIB ORDER=NTTU.SYS.PROCLIB //*=====================================================================//* °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°° //* DB2 LOAD //* °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°° //*=============================================================//*//*------------------------------------------------------------------*/ //* T00101 //* --------------------------------------------------------------------/* //T00101R EXEC DSNUPROC,PARM='DB2O,I650001T001012' //DSNUPROC.SYSIN DD * RUNSTATS TABLESPACE D20015.S001501 TABLE (ALL) INDEX (ALL) /*//*

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