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ee Administration

/ Embedded SQL

by: Glen Orsburn

Chapter 6

Database Administration

• Views

• Security using Grant and Revoke

• Creating an Index

• Advantages /Disadvantages

• SQL Catalog

• Integrity

Views• Create view Database as

Select packid, packname, packcost from package where packtype = ‘Database’

• When we do the following...Select * from Database where

packcost > 400The SQL engine translates the select of the view to the original select.

Select packid, packname, packcost from package where packtype = ‘Database’

and packcost > 400

Creating a view and change column names.

• Create view Database (pkid, name, cost) asSelect packid, packname, packcost

from package where packtype = ‘Database’

• Prompt F4 --

Specify CREATE VIEW Statement

Type choices, press Enter.

View . . . . . . . . . softpack Name Library . . . . . . goolib Name, F4 for list

Field names for view 1 1=Use result file names 2=Specify names

WITH CHECK OPTION . . 1 1=NONE 2=CASCADED

3=LOCAL CHECK OPTION is a validity check that can be placed in SQL views. The possible choices are: CASCADED check specifies the constraint LOCAL conform to the definition of that view

Views - Advantages

• Views provide data independence. If the underlying table structure is to change, a view may still be created that would emulate the original structure.

• The same data can be viewed by different users in different ways.

• A view should only contain the information a given user or group needs to see.

Views - Disadvantages

• Views can be difficult to impossible to update without violating referential integrity.

• Many systems do not allow updates of a view that incorporates a join.

Removing a View

• SyntaxDrop view Database

http://publib.boulder.ibm.com/pubs/html/as400/online/v4r3eng.htm

Security

• Grant - This command allows a user to access a particular object.

• Revoke - This command disallows a user to access a particular object.

• Syntax...Grant operation on object to user

– Operation can be select, insert, update, delete, index, alter or all.

– Object is a table, view or stored procedure– User is the UserID

Indexes

• Speeds access to records by keeping track of row numbers for a selected attribute (or set of attributes) .

• Advantage - Increases speed to access specific data points.

• Disadvantage - Slows updates, inserts and deletes due to overhead of updating index table and data table.

Index Syntax

• Create [unique] index ind_packid on package (packid)

• An index may be made from more than one field...

Create index ind_empname on employee(firstname, lastname)

• To drop an index...Drop Index indexname

Optional Index Name Table field to index

System Catalog

• A set of related tables that define all objects in the database.– SYSTABLES - Information about all of the

tables in the database (name, creator, creation date…)

– SYSCOLUMNS -Information about the columns within the tables (datatypes, length, null allowed…)

– SYSINDEXES - Information about the indexes on the tables (attribute being indexed, unique

select * from syscolumns

SYSCHKCST *FILE LF 24576 SQL catalog view SYSCOLUMNS *FILE LF 49152 SQL catalog view SYSCST *FILE LF 49152 SQL catalog view SYSCSTCOL *FILE LF 40960 SQL catalog view SYSCSTDEP *FILE LF 40960 SQL catalog view SYSINDEXES *FILE LF 65536 SQL catalog view SYSKEYCST *FILE LF 69632 SQL catalog view SYSKEYS *FILE LF 49152 SQL catalog view SYSPACKAGE *FILE LF 69632 SQL catalog view SYSREFCST *FILE LF 40960 SQL catalog view SYSTABLES *FILE LF 40960 SQL catalog view SYSVIEWDEP *FILE LF 65536 SQL catalog view SYSVIEWS *FILE LF 36864 SQL catalog view

System Catalog - Views

Database Integrity

• IEF - Integrity Enhancement Feature. An ANSI standard for supporting integrity.

• The following are added to the ‘create table ‘ SQL.– Check (location IN (‘Accounting’, ‘Sales’,

‘Home’))– Primary Key (tagnum)– Foreign Key (compid) references computer

Integrity ExampleCREATE TABLE pc

(tagnum char(5),

compid char(4),

empnum decimal(3,0),

location char(12),

CHECK (location IN (‘Accounting’, ‘Sales’, ‘Home’))

PRIMARY KEY (tagnum)

FOREIGN KEY (compid) REFERENCES computer

HLL

- Similar statement we have been using in ISQL (Interactive SQL)