Oracle_ch13.pptx

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Dr. Chen, Oracle Database System (Oracle) 1

Chapter 13Views

(up to p.495)

Jason C. H. Chen,Ph.D.

Professor of MIS

School of BusinessGonzaga University

Spokane, WA 99258 USA

[email protected]


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Objectives

Create a view by using CREATE VIEW command orthe CREATE OR REPLACE VIEW command

Employ the FORCE and NOFORCE options

State the purpose of the WITH CHECK OPTIONconstraint

Explain the effect of the WITH READ ONLY option

Update a record in a simple view

Re-create a view


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Objectives (continued)

Explain the implication of an expression in aview for DML operations

Update a record in a complex view Identify problems associated with adding records

to a complex view Identify the key-preserved table underlying a

complex view Drop a view

Explain inline views and the use of ROWNUMto perform a TOP-N analysis

Create a materialized view to replicate data


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Database Views

Table-1 Table-NTable-2

database

Single view table

Query

Output:

Report, Graphs

Database view

A database view is

a logical (virtual)

table based on a

query.

It does not

store data, but

presents it in aformat

different from

the one in

which it is

stored in theunderlying

tables.

With the database view,

you can view database

records, but you cant

insert new records or

modify or delete exiting

records.


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Views

Permanent objects (logical or virtual table)that store queries but nodata

Based on a source query that: can specify a subset of a single tables fields or records

can join multiple tables

Two purposes

Reduce complex query requirements

Restrict users access to sensitive data (enforce

security; user has access to view but not

underlying table)


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Creating and Using Database Views

Views can be updateable if: SELECT clause contains only fieldnames, no functions

or calculations

cannot contain the ORDER BY, DISTINCT, or

GROUP BY clauses, group functions, or set operators search condition cannot contain a nested query

Views are used like tables for selecting, inserting,

updating and deleting data (only updatable views canbe modified)


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Database View (cont.)

SELECT view_name FROM user_views;

SELECT view_name FROM ALL_VIEWS

WHERE owner=SYSTEM;

DROP VIEW;

CREATEORREPLACE VIEW AS

;


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Creating a Simple View

Only references one tableno group functions,

GROUP BY clause, or expressions

Figure 13-4 Selecting all records from the INVENTORY view

-- chapter 13, Figure 13-4(b); p.477

CREATE VIEW books_inventory_vu

AS SELECT isbn, title, retail price

FROM booksWITH READ ONLY;

SELECT *

FROM books_inventory_vu;

-- chapter 13, Figure 13-4; p.477

CREATE VIEW inventory

AS SELECT isbn, title, retail price

FROM booksWITH READ ONLY;

SELECT *

FROM inventory;

DROP VIEW inventory;

SELECT *

FROM inventory;

What happen to

Database after

DROP view?

SELECT *

FROM books;

-- REcreate inventory view


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CREATE OR REPLACE VIEW book_vu AS

SELECT isbn, title, categoryFROM books

WHERE category = 'COOKING';

SELECT *FROM book_vu;


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Figure 13-1 View Processing


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Types of Views

Table 13-1 Overview of View Concepts


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I. Creating a View

You use the CREATE VIEWkeywords to create a view

Use OR REPLACE if the view already exists

Use FORCE if the underlying table does not exist at the timeof creation

Provide new column names if necessary

WITH CHECK OPTION constraintif used, prevents data

changes that will make the data subsequently inaccessible to

the view

WITH READ ONLYprevents DML operations

Figure 13-2 Syntax of the CREATE VIEW command


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Database View

What are gains?

--EXTRA for VIEW

SELECT firstname || || lastname, order#, orderdate

FROM customers_vu, orders

WHERE customers_vu.customer# = orders.order#;

DELETING VIEWSDROP VIEW viewname;

DROP VIEW customers_vu;

CREATE VIEW AS

;e.g.,

SELECT view_name FROM user_views;

CREATEOR REPLACE VIEWcustomers_vu ASSELECT customer#, lastname, firstname, regionFROM customers;


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DML Operations on a Simple View

Any DML operations are allowed through simple

views unless created with WITH READ ONLY

option

DML operations that violate constraints on the

underlying table are not allowed


CREATE VIEW region_ne

AS SELECT *

FROM customersWHERE region = 'NE';

SELECT customer#, lastname, city, state, region

FROM region_ne;


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Why Failed to Update?

-- chapter 13, Figure 13-6; p.479UPDATE inventory

SET price = 45.96

WHERE title LIKE '%POEM';

SELECT *

FROM inventory

WHERE title LIKE '%POEM%';

UPDATE inventory

SET title = 'THE SHORTEST POEMS'

WHERE title LIKE '%POEM%';

Figure 13-6 Failed updates on the INVENTORY view


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CREATE OR REPLACE VIEW inventoryAS SELECT isbn, title, retail price

FROM books;

SELECT *

FROM inventoryWHERE title LIKE '%BODYBUILD%';


UPDATE inventory

SET price = 49.95

WHERE title LIKE '%BODYBUILD%';

SELECT *

FROM inventory


SELECT *FROM books


DML Operations on a Simple View (continued)


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Rule for DML operations

As long as the view isnt created with the WITH

READ ONLY option and any DML operation is

allowed if it doesnt violate an existing constraint

on the underlying table.

You can add, modify, and even delete data in anunderlying table as long as one of the following

constraints doesnt prevent the operation:

PRIMARY KEY - FOREIGN KEY

UNIQUE - NOT NULL

WITH CHECK OPTIONPractice Figure 13-9 to

13-11 (pp.482-483)


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Exercises

Practice all the examples in the text.

A Script file is available on the Bb (file

name: ch13Queries.sql)

After completing all examples, do the HW.

In-class Exercise

#1 (p.508)


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Homework - Hands-On Assignments

Read and Practice all examples on Chapters 13

1. Read Oracle assignment and create a script fileOracle_ch13_Lname_Fname.sql for questions (#1-5and 9,10; p.508) on Hands-on Assignments.

2. Execute and test one problem at a time and make surethey are all running successfully.

3. When you done, spool the script files (see next slidefor spooling instructions) and email the file(Oracle_ch13_Spool_Lname_Fname.txt) to me by themidnight before the next class.

Email me with one attachment

(Oracle_ch13_Spool_Lname_Fname.) to:

[email protected] subject title of

bmis441_Oracle_ch13 or mbus699_Oracle_ch13


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How to Spool your Script and Output Files

After you tested the script file of Oracle_ch13_Lname_Fname.sqlsuccessfully, follow the instructions below to spool both script and output

files:Step 0. Run the following script file from SQL*Plus (since you have created

JLDB tables)

1. type the following on SQL> Spool c:\oradata\Oracle_ch13B_Spool_Lname_Fname.txt(make sure your name is

entered)

2. open Oracle_ch13_Lname_Fname.sql that you already tested

3. copy and paste all the SQL commands (including all comments) to theSQL*PLUS

4. type Spool Off on the SQL>

The output should contain your personal information, all SQL commands andtheir solution on the .txt file and saved in C: drive (oradata\ folder)

Email me with the spooled file (.txt) with attachment to:

[email protected]

with subject title of

bmis441_Oracle_ch13 or mbus699_Oracle_ch13


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PART II


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II. Creating a Complex View

A complex view may contain data from multipletables or data created with the GROUP BY clause,

functions, or expressions

Type of DML operations allowed depends on

various factors


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DML Operations on a Complex View with an Arithmetic Expression

Figure 13-12 Create and update a complex view named prices


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Rule#1:

DML

operations

are not

permitted ifthe view

includes a

column

based on

arithmetic

expression

Figure 13-14 Failed attempts to add a new book via the PRICES view


INSERT INTO prices (isbn, title, cost, retail)

VALUES(0202020202, 'A New Book', 8.95, 15.95);


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Dr. Chen, Oracle Database System (Oracle) 25Figure 13-16 Constraint violation with an INSERT command via the PRICES view

no pubid is

inserted

Rule#2:

DML

operations

are not

permitted ifthey violate

a constraint

such as NOT

NULL,

UNIQUE

etc.


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DML Operations on a Complex View Containing Data

from Multiple Tables

DML operations cannot be performed on non-key-preserved

tables, but they are permitted on key-preserved tables

Figure 13-17 PRICES view with a table joinPractice: Figure 13-18


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DML Operations on a Complex View Containing Data

from Multiple Tables (continued)

Figure 13-19 Failed attempt to update the publisher name via the PRICES view

Rule#3:

DMLoperations

cant be

performed

on a non-key-

preserved

table.


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DML Operations on a Complex View Containing

Functions or Grouped Data

Rule#4: DML operations are notpermitted if the view

includes a group function or a GROUP BY clause, theDISTINCT keyword, or the ROWNUM pseudocolumn.

Figure 13-21 View including grouped data


CREATE VIEW balancedue

AS SELECT customer#, order#, SUM(quantity * retail) AmtdueFROM customers JOIN orders USING (customer#)

JOIN orderitems USING (order#)

JOIN books USING (isbn)

GROUP BY customer#, order#;

SELECT *

FROM balancedue;


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SELECT *

FROM balancedue;

Figure 13-21 View

including grouped data


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DML Operations on a Complex View Containing

Functions or Grouped Data (continued)

Figure 13-22 Failed DELETE command on a view with grouped data


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Dropping a View

Use DROP VIEW command

Figure 13-25 Command to drop the PRICES view


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III. Creating an Inline View

An inline view is a temporary table createdby using a subquery in the FROM clause

It can only be referenced while the

command is being executed

Most common usageTOP-N analysis


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TOP-N Analysis

ORDER BY included to identify top values:Descending for highest values

Ascending for lowest values

Extract data based on ROWNUM

Figure 13-26 Syntax of TOP-N analysis


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TOP-N Analysis (continued)

Figure 13-28 TOP-N analysis to identify the five most profitable books


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Figure 13-28 TOP-N analysis to identify the five

most profitable booksFigure 13-28 TOP-N analysis to determine the three

lest profitable books


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PART III


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Materialized Views

Replicate data

Store data retrieved from view query

Referred to as snapshots


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Materialized Views (continued)

Figure 13-30 Creating a materialized view named CUSTBAL_MV


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Figure 13-31 Query a

materialized view


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Materialized Views (continued)

Figure 13-32 Drop a materialized view


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Summary

A view is a temporary or virtual table that is used toretrieve data that exists in the underlying database tables

The view query must be executed each time the view is

used

A view can be used to simplify queries or to restrict accessto sensitive data

A view is created with the CREATE VIEW command

A view cannot be modified; to change a view, it must be

dropped and then re-created, or the CREATE ORREPLACE VIEW command must be used


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Summary (continued)

Any DML operation can be performed on a simple query if itdoes not violate a constraint

A view that contains expressions or functions, or that joins

multiple tables, is considered a complex view A complex view can be used to update only one table; the

table must be a key-preserved table

Data cannot be added to a view column that contains anexpression

DML operations are not permitted on non-key-preservedtables


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Summary (continued)

DML operations are not permitted on views that include groupfunctions, a GROUP BY clause, the ROWNUM pseudocolumn, or theDISTINCT keyword

Oracle 11g assigns a row number to every row in a table to indicate itsposition in the table; the row number can be referenced by the keywordROWNUM

A view can be dropped with the DROPVIEW command; the data isnot affected, because it exists in the original tables

An inline view can be used only by the current statement and caninclude an ORDER BY clause

TOP-N analysis uses the row number of sorted data to determine a

range of top values Materialized views physically store view query results

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