TBRUG Deep Dive into New DB2 V8 SQL and Features February 2009

© 2008 IBM Corporation

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TBRUG Deep Dive into New DB2 V8 SQL and Features February 2009

Frank MerinoSr. IT SpecialistDB2 for z/OS [email protected]

IBM Software Group | Information Management software

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DB2 V8 LNL … Agenda

Multi-row FETCH

Multi-row INSERT

GET DIAGNOSTICS

Common table expression (CTE)

Sequence objects

INSERT within SELECT

Materialized Query Table (MQT)

Additional SQL Enhancements

Documentation

Questions


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Multi-Row FETCH and INSERT

What are they?

– Multi-row FETCH:• The ability to retrieve multiple rows of data as a rowset.

– Rowset: A group of rows that are grouped together and operated on as a set.

– Multi-row INSERT:• The ability to insert one or more rows.• Like the INSERT INTO… SELECT FROM, except using a

VALUES clause.

– Both can be used in static and dynamic SQL


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Multi-row FETCH … Syntax

DECLARE CURSOR Syntax:DECLARE cursor-name CURSOR

WITH ROWSET POSITIONINGFOR SELECT select-statement

NOTES:• WITH ROWSET POSITIONING defines whether multiple rows can be

retrieved as a rowset on a single FETCH• Default is WITHOUT ROWSET POSITIONING


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Multi-row FETCH … Syntax (continued)

FETCH Syntax:FETCH NEXT ROWSET

PRIOR ROWSETFIRST ROWSETLAST ROWSETCURRENT ROWSETROWSET STARTING AT ABSOLUTE host-variable or integer-value

RELATIVE

FROM cursor-name FOR host-variable ROWS INTO host-variable-arrayinteger-value

NOTE: The rowset-positioned clauses specify cursor positioning like the existing row-positioned clauses NEXT, PRIOR, FIRST, LAST, CURRENT, ABSOLUTE and RELATIVE.


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Multi-row FETCH … Notes

Recommend always coding the FOR n ROWS clause, which controls the number of rows retrieved by a FETCH.

FETCH FIRST n ROWS ONLY clause can be coded in the SELECT. However, this controls the total number of rows that can retrieved. SQLCODE +100 will occur if attempt to retrieve beyond the numberspecified.

Host-variable-array:– One array per column being retrieved.

– Size needs to be large enough to hold number of rows retrieved.

– Null indicator array needed to handle nulls, and size must equal column array.

Locks are held on all rows in rowset depending on isolation level.


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Multi-row FETCH … Examples

Given cursor C1 is defined as:DECLARE C1 CURSOR WITH ROWSET POSITIONING

FOR SELECT COL1, COL2 FROM T1

Fetch 5 rows from the current cursor position:FETCH NEXT ROWSET FROM C1 FOR 5 ROWS INTO :HVA1,:HVA2

Fetch 5 rows starting with row 20 regardless of the current position of the cursor, and cause the cursor to be positioned on that rowset at the completion of the fetch:

FETCH ROWSET STARTING AT ABSOLUTE 20 FROM C1 FOR 5 ROWS INTO :HVA1,:HVA2

Fetch the previous rowset, and have the cursor positioned on that rowset:FETCH PRIOR ROWSET FROM C1 FOR 5 ROWS INTO :HVA1,:HVA2 … or …FETCH ROWSET STARTING AT RELATIVE -5 FROM C1 FOR 3 ROWS INTO :HVA1,:HVA2

Fetch the first 5 rows and leave the cursor positioned on that rowset at the completion of the fetch:

FETCH FIRST ROWSET FROM C1 FOR 5 ROWS INTO :HVA1,:HVA2


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Multi-row FETCH … Cursor Positioning


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Multi-row FETCH … Cursor Positioning - Partial Rowset


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Multi-row FETCH … COBOL ExampleDeclare cursor C1 and fetch 10 rows using a multi-row FETCH statement

01 OUTPUT-VARS.05 NAME OCCURS 10 TIMES.

49 NAME-LEN PIC S9(4) USAGE COMP.49 NAME-TEXT PIC X(40).

05 SERIAL-NUMBER PIC S9(9) USAGE COMP OCCURS 10 TIMES.01 IND-VARS.

10 INDSTRUC1 PIC S9(4) USAGE COMP OCCURS 10 TIMES.10 INDSTRUC2 PIC S9(4) USAGE COMP OCCURS 10 TIMES.

PROCEDURE DIVISION.EXEC SQL

DECLARE C1 SCROLL CURSOR WITH ROWSET POSITIONING FORSELECT NAME, SERIAL# FROM EMPLOYEE

END-EXEC.EXEC SQL OPEN C1 END-EXEC.EXEC SQL

FETCH FIRST ROWSET FROM C1 FOR 10 ROWSINTO :NAME:INDSTRUC1,:SERIAL-NUMBER:INDSTRUC2

END-EXEC.


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Multi-row FETCH … Positioned UPDATE

Syntax:UPDATE table-name SET assignment-clause

WHERE CURRENT OF cursor-name

FOR ROW host-variable OF ROWSETinteger-value

Examples: (Cursor CS1 positioned on a 10 row rowset of table T1.)– Following statement updates all 10 rows of the rowset:

UPDATE T1 SET C1 = 5 WHERE CURRENT OF CS1

– Following statement updates row 4 of the rowset:UPDATE T1 SET COL1='ABC‘ WHERE CURRENT OF CS1 FOR ROW 4 OF

ROWSET


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Multi-row FETCH … Positioned DELETE

Syntax:DELETE FROM table-name

WHERE CURRENT OF cursor-name

FOR ROW host-variable OF ROWSETinteger-value

Examples: (Cursor CS1 positioned on a 10 row rowset of table T1.)– Following statement deletes all 10 rows of the rowset:

DELETE FROM T1 WHERE CURRENT OF CS1

– Following statement deletes row 4 of the rowset:DELETE FROM T1 WHERE CURRENT OF CS1 FOR ROW 4 OF ROWSET


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Multi-row INSERT … Syntax

INSERT Syntax:INSERT INTO table-name (column-name1, etc)

FOR host-variable ROWS integer-value

VALUES ( expression or host-variable-array or NULL or DEFAULT, etc.)

ATOMIC or NOT ATOMIC CONTINUE ON SQLEXCEPTION

NOTES:– Same rules apply for host-variable-array as with FETCH– For dynamic statements:

• FOR n ROWS specified on EXECUTE statement• ATOMIC/NOT ATOMIC CONTINUE ON SQLEXCEPTION specified on PREPARE

statement


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Multi-row INSERT … ATOMIC/NOT ATOMIC…

ATOMIC (default):If any insert fails, all changes are undone.

NOT ATOMIC CONTINUE ON SQLEXCEPTION– Allows processing to continue if any insert fails

– Use GET DIAGNOSTICS to examine failure by row

– SQLCODEs & SQLSTATEs:• All inserts failed: SQLCODE -254 & SQLSTATE 22530• All inserts successful, but warnings: SQLCODE +252 & SQLSTATE 01659• At least one insert failed: SQLCODE -253 & SQLSTATE 22529


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Multi-row INSERT … Examples

Insert 10 rows of data into table with 2 columns:INSERT INTO T1 (C1, C2) FOR 10 ROWSVALUES (:hva1:hvaind1, :hva2:hvaind2)NOT ATOMIC CONTINUE ON SQLEXCEPTION

Insert a variable number of rows for a column in a table:INSERT INTO T1 FOR :hv ROWSVALUES (:hva:hvaind) ATOMIC

Note: SQLCODE -246 & SQLSTATE 42873 returned if host-variable- array has fewer entries than specified by :hv. On the other hand, if array has more, excess is ignored.


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GET DIAGNOSTICS

Enables applications to retrieve diagnostic information.

Complements and extends diagnostics available in the SQLCA.

Can be used in conjunction with or instead of the SQLCA to interrogate the results of SQL statements.

Is especially important when using multi-row INSERT with NOT ATOMIC CONTINUE ON SQLEXCEPTION.

Can only be embedded in an application program.


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GET DIAGNOSTICS … Syntax

GET DIAGNOSTICS statement-information

condition-informationcombined–information

statement-information:host-variable = DB2_LAST_ROW

DB2_SQL_ATTR_CURSOR_ROWSETNUMBERROW_COUNT


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GET DIAGNOSTICS … Syntax (continued)



condition-information:CONDITION host-variable or integer

host-variable = DB2_RETURNED_SQLCODEDB2_ROW_NUMBERDB2_SQLERRD1 – 6DB2_ORDINAL_TOKEN_nDB2_TOKEN_COUNT


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GET DIAGNOSTICS … Syntax (continued)



combined-information:host-variable = ALL STATEMENT

CONDITION blank or host-variable or integer


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GET DIAGNOSTICS … ExamplesTo determine how many rows were updated in an UPDATE statement

GET DIAGNOSTICS :rcount = ROW_COUNT;

To handle multiple SQL errors during a NOT ATOMIC multi-row INSERTGET DIAGNOSTICS :numerrors = NUMBER;

– Then code a loop to execute the following for the number of errorsGET DIAGNOSTICS CONDITION :i :retstate = DB2_RETURNED_SQLCODE

To see all diagnostic information for an SQL statementGET DIAGNOSTICS :diags = ALL STATEMENT

Sample output in :diagsNumber=1; Returned_SQLSTATE=02000; DB2_RETURNED_SQLCODE=+100;– Would continue for all applicable items and for all conditions– Items are delimited by semicolons


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GET DIAGNOSTICS … Examples (continued)

Assume a multi-row INSERT of 10 rows is performed on table T1 with 2 columns (C1/smallint & C2/integer ). All but 2 rows are inserted, cause values are invalid.

INSERT INTO T1 (C1, C2) FOR 10 ROWS VALUES (:hva1:hvind1, :hva2:hvind2) NOT ATOMIC CONTINUE ON SQLEXCEPTION;

After execution of the INSERT statement, SQLCA shows:SQLCODE = 0SQLSTATE = 0SQLERRD3 = 8


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GET DIAGNOSTICS … Examples (continued)

SQLCA shows only 8 rows inserted. Using the following GET DIAGNOSTICS statements the following can be determined:

GET DIAGNOSTICS :num_rows = ROW_COUNT, :num_cond = NUMBER;

Would result in NUM_ROW = 8 and NUM_COND = 2 (2 conditions)

GET DIAGNOSTICS CONDITION 1 :sqlstate = RETURNED_SQLSTATE,:sqlcode = DB2_RETURNED_SQLCODE, :row_num = DB2_ROW_NUMBER;

Could result in SQLSTATE = 22003, SQLCODE = -302, and ROW_NUM = 4

GET DIAGNOSTICS CONDITION 2 :sqlstate = RETURNED_SQLSTATE,:sqlcode = DB2_RETURNED_SQLCODE, :row_num = DB2_ROW_NUMBER;

Could result in SQLSTATE = 22003, SQLCODE = -302, and ROW_NUM = 8


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Common table expression (CTE)

Are introduced by the WITH keyword at the beginning of a query.

Multiple CTEs can be coded, and are separated by a comma.

Can be reference elsewhere in the query, including by other CTEs.

Help simplify the coding of a complex query that could otherwise need nested table expressions.

Avoids the need to create and maintain views.

Like a view, columns names for the CTE are specified in parentheses after the CTE name.

No AS clause required for calculated columns in the SELECT.

Are materialized if referenced more than once.


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Common table expression (CTE) … ExampleWITH

E AS (SELECT EMPNO, LASTNAME, SALARY, SUBSTR(CHAR(HIREDATE,ISO),1,3) CONCAT '0 - 9‘ AS HIREDECADEFROM EMPLOYEE),

M (HIREDECADE, MINIMUM_SALARY) AS (SELECT HIREDECADE, MIN(SALARY)FROM EGROUP BY HIREDECADE)

SELECT E.EMPNO, E.LASTNAME, E.HIREDECADE,E.SALARY, M.MINIMUM_SALARYFROM E INNER JOIN MON E.HIREDECADE = M.HIREDECADE


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Sequence objects

Stand-alone objects and are not tied to a table like an identity column.

Unlike an identity column which has a one to one relationship to a table, a sequence can be used for many tables or many sequences can be used in a table.

Avoids the concurrency and performance when applications generate their own sequence numbers.

Allows multiple transactions to concurrently access and increment number, and still guarantee each will be unique, without having to wait for one transaction to commit before allowing another.


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Sequence objects (continued)

Defined using SQL DDL statements and attributes are similar to those for identity columns.

Data type for values generated can be smallint, integer and decimal with a zero scale.

All attributes, except the data type, can be altered at any time via the ALTER SEQUENCE statement, as needed.

Value retrieved via the NEXT VALUE FOR or PREVIOUS VALUE FOR expressions. A ROLLBACK has no effect on the value retrieved.


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Sequence objects … NEXT and PREVIOUS VALUE

Applications refer to the sequence object by its name.– NEXT VALUE FOR sequence-name– PREVIOUS VALUE FOR sequence-name

Can be invoked during:– SELECT statement or SELECT INTO statement– INSERT statement within VALUES clause– INSERT statement within select-clause of fullselect– UPDATE statement with SET clause (except NEXT VALUE cannot be in

select-clause)– VALUES or VALUES INTO statement– CREATE PROCEDURE, FUNCTION TRIGGER– SET host-variable-assignment statement


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Sequence objects … ExamplesAssume sequence created with START WITH 1, INCREMENT BY 1SELECT NEXT VALUE FOR SQ1 FROM SYSIBM.SYSDUMMY1; Generates Value of 1SELECT NEXT VALUE FOR SQ1 FROM SYSIBM.SYSDUMMY1; Generates Value of 2COMMIT;SELECT PREVIOUS VALUE FOR SQ1 FROM SYSIBM.SYSDUMMY1;

Returns most recently generated value (2)

Specified within SET clause of UPDATE statementUPDATE T1 SET C1 = (SELECT PREVIOUS VALUE FOR SQ1 FROM T);UPDATE T1 SET C1 = NEXT VALUE FOR SQ1;

Specified within VALUES clause of INSERT statementINSERT INTO T1 (COL1, COL2, COL3)VALUES ( NEXT VALUE FOR SQ1, NEXT VALUE FOR SQ2, :hval1 )


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INSERT within SELECT

Provides the capability of retrieving column values inserted by DB2 such as:– Identity columns and sequence object values– User-defined defaults and expressions– Columns modified by BEFORE INSERT triggers– ROWIDs

Retrieve rows in the sequence as they were inserted with ORDER BY INPUT SEQUENCE

Benefits include:– Reduced network costs– Simplified procedural logic in stored procedures


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INSERT within SELECT … Examples

Retrieve inserted sequence values:SELECT * FROM FINAL TABLE(INSERT INTO T1 (COL1, COL2, COL3)VALUES ( NEXT VALUE FOR SQ1, NEXT VALUE FOR SQ2, :hval1 ))

Retrieve rows in sequence they are inserted:DECLARE CS2 SCROLL CURSOR WITH ROWSET POSITIONING FORSELECT EMPNO FROM FINAL TABLE(INSERT INTO EMPLOYEE (NAME, TELE)FOR 3 ROWS VALUES(:HVA1, :HVA2))ORDER BY INPUT SEQUENCE


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Materialized Query Table (MQT)

What is it?– Table containing materialized data derived, usually from complex

aggregated functions, from one or more source tables, which can be base tables, views, or table expressions.

– MQTs can be accessed directly or chosen by the optimzer (through automatic query rewrite) when base table or view is referenced.

– Two types:• System maintained using REFRESH TABLE statement• User maintained using functions like LOAD utility, INSERT, UPDATE,

DELETE and can use REFRESH TABLE statement.– Can be created from scratch or an existing tables can be registered

as an MQT.– Identified in SYSIBM.SYSTABLES as TYPE ‘M’.


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Materialized Query Table (MQT) … CREATE Syntax

CREATE TABLE MQT1 AS (fullselect)

DATA INITIALLY DEFERRED

REFRESH DEFERRED

MAINTAINED BY SYSTEM/USER

ENABLE/DISABLE QUERY OPTIMIZATION

NOTE: ENABLE/DISABLE QUERY OPTIMIZATION controls exploitation of automatic query rewrite.


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Materialized Query Table (MQT) … CREATE Example

CREATE TABLE MQT1 AS (SELECT T.PDATE, T.TRANSID,SUM(QTY * PRICE) AS TOTVAL,COUNT(QTY * PRICE) AS CNTFROM SCNDSTAR.TRANSITEM TI, SCNDSTAR.TRANS TWHERE TI.TRANSID = T.TRANSIDGROUP BY T.PDATE, T.TRANSID)

DATA INITIALLY DEFERREDREFRESH DEFERREDMAINTAINED BY SYSTEMENABLE QUERY OPTIMIZATIONIN MYDBMQT.MYTSMQT;


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Materialized Query Table (MQT) … ALTER Syntax

ALTER syntax to register an existing table as an MQT:

ALTER TABLE T1 ADD MATERIALIZED QUERY (fullselect)DATA INITIALLY DEFERREDREFRESH DEFERREDMAINTAINED BY SYSTEM/USERENABLE/DISABLE QUERY OPTIMIZATION


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Materialized Query Table (MQT) … ALTER Example

ALTER TABLE T1 ADD MATERIALIZED QUERY (SELECT T.PDATE,SUM(QTY * PRICE) AS TOTVAL,COUNT(QTY * PRICE) AS CNTFROM SCNDSTAR.TRANSITEM TI, SCNDSTAR.TRANS TWHERE TI.TRANSID = T.TRANSIDGROUP BY T.PDATE)

DATA INITIALLY DEFERREDREFRESH DEFERREDMAINTAINED BY USERENABLE QUERY OPTIMIZATION;


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Materialized Query Table … Populate & Refresh

Ensure data currency meets user requirements.

Issuing REFRESH TABLE statement periodically:– Deletes all rows in MQT– Executes the fullselect– Inserts calculated data– Updates the catalog with refresh timestamp and cardinality– Executes in a single UOW– Consider logging and performance impact

For user-maintained, other methods like LOAD, Insert and Update, can be used.


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Materialized Query Table … Automatic Query Rewrite

Two special registers control whether automatic query rewrite is enabled at the application level.– CURRENT REFRESH AGE = 0 or ANY

• 0 – No MQTs considered• ANY – All MQTs considered

– CURRENT MAINTAINED TABLE TYPES FOR OPTIMIZATION =ALL/NONE/SYSTEM/USER• ALL – All MQTs considered• NONE – No MQTs considered• SYSTEM – Only system-maintained MQTs considered• USER – Only user-maintained MQTs considered

Two DSNZPARMs (REFSHAGE & MAINTYPE) provide defaults for above registers.


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Materialized Query Table … Admin & Considerations

Information about MQTs is stored in SYSIBM.SYSVIEWS.

No primary keys or unique indexes or triggers are allowed for MQTs.

MQTs and their indexes are dropped if their associated base tables are dropped.

Design issue:– Few generic MQTs or more specialized MQTs

– Consider trade off between performance and maintenance.


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Additional SQL Enhancements

GROUP BY expression:SELECT SUBSTR(CHAR(HIREDATE,ISO),1,3)CONCAT '0 - 9' AS HIREDECADE,MIN(SALARY) AS MINIMUM_SALARYFROM EMPLOYEEGROUP BY SUBSTR(CHAR(HIREDATE,ISO),1,3)CONCAT '0 - 9‘

Multiple DISTINCT clauses on different columns:SELECT COUNT(DISTINCT C1), SUM(DISTINCT C2) FROM T1;


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DocumentationDB2 V8 for z/OS Manuals:– http://www-1.ibm.com/support/docview.wss?rs=64&uid=swg27011659

Redbooks:– DB2 V8 for z/OS Everything You Ever Wanted to Know… and More

• http://publib-b.boulder.ibm.com/abstracts/sg246079.html?Open– DB2 V8 for z/OS Performance Topics

• http://publib-b.boulder.ibm.com/abstracts/sg246465.html?Open

DB2 for z/OS Library: (links to additional document for DB2 V8 for z/OS)

– http://www-306.ibm.com/software/sw- library/en_US/products/L374840M53366O19/

http://www-1.ibm.com/support/docview.wss?rs=64&uid=swg27011658

http://publib-b.boulder.ibm.com/abstracts/sg246079.html?Open

http://publib-b.boulder.ibm.com/abstracts/sg246465.html?Open

http://www-306.ibm.com/software/sw-library/en_US/products/L374840M53366O19/

http://www-306.ibm.com/software/sw-library/en_US/products/L374840M53366O19/


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Questions???

TBRUG Deep Dive into New DB2 V8 SQL and Features February 2009

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