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A Guide to SQL, Sixth Edition

Chapter 6Database Administration

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Objectives

Understand, create, and drop views

Recognize the benefits of using views

Grant and revoke users' database privileges

Understand the purpose, advantages, and disadvantages of using an index

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Objectives

Create, use, and drop an index

Understand and obtain information from the system catalog

Use integrity constraints to control data entry

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Introduction

Database administrationThe process of managing a database

Database administratorA person or an entire group charged with

managing the database

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Views

Base tablesExisting, permanent tables in a relational

database

ViewA derived table where data is derived from

a base tableUser interacts with the viewView provides security

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Views

A view is defined by creating a defining query

A defining query is a SQL command that indicates the rows and columns that will appear in the view

To create a view definition, use the CREATE VIEW command

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Views

When a query involves a view, SQL changes the query to select data from the table(s) in the database that created the view

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ViewsThe use of views provides several benefitsViews provide data independenceThe display of data can be customized to

meet each user’s needsA view contains only those columns required

by a given user, which has two advantages:A view greatly simplifies the user’s perception of

the databaseViews provide a measure of security

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Row-and-Column Subsets

A row-and-column subset view that contains the primary key of the underlying base table is updateable

Figure 6.9 illustrates a view that contains serious update problems due to the exclusion of the primary key

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Row-and-Column Subsets

Figure 6.9

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Joins

In general, views that involve joins of base tables can cause problems at update

If two base tables have the same primary key and the primary key is used as the join column, updating the database is not a problem

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Statistics

CRED_CUST view contains the most troublesome view of all because it involves statistics calculated from one or more base tables

Rows cannot be added to a view that includes calculations

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Dropping a View

When a view is no longer needed, remove it by using the DROP VIEW command

Example:DROP VIEW HSEWRES;

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Security

Security is the prevention of unauthorized access to the database

Two security mechanisms:ViewsGRANT command

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Security

The database administrator can grant different types of privileges to users and then revoke them later, if necessary

User privileges can be granted and revoked using the GRANT and REVOKE commands, respectively

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Security

Problem:User Johnson must be able to retrieve data

from the REP table.

Solution:GRANT SELECT ON REP TO JOHNSON;

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Security

The privileges that can be granted are:SELECT to retrieve dateUPDATE to change dataDELETE to delete data INSERT to add new data INDEX to create an indexALTER to change the table structure

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Security

The REVOKE command is used to revoke privileges from users

Problem:User Johnson is no longer allowed to

retrieve data from the REP table.

Solution:REVOKE SELECT ON REP FROM JOHNSON;

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Indexes

An index can be created for any column or combination of columns in any table

After creating an index, the DBMS uses it to speed up data retrieval

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Indexes

AdvantagesMakes certain types of retrieval more

efficient

DisadvantagesOccupies disk space and is technically

unnecessaryMust be updated whenever corresponding

data in the database is updated

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Creating an Index

Problem: Create an index named BALIND on the BALANCE

column in the CUSTOMER table. Create an index named REPNAME on the

combination of the LAST_NAME and FIRST_NAME columns in the REP table.

Create an index named CREDNAME on the combination of the CREDIT_LIMIT and CUSTOMER_NAME columns in the CUSTOMER table, with the credit limits listed in descending order.

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Creating an Index

Solution:CREATE INDEX BALIND ON CUSTOMER(BALANCE); CREATE INDEX REPNAME ON REP(LAST_NAME, FIRST_NAME); CREATE INDEX CREDNAME ON CUSTOMER(CREDIT_LIMIT DESC, CUSTOMER_NAME);

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Dropping an Index

The command used to drop (delete) an index is DROP INDEX

Problem:Delete the CREDNAME index

Solution:DROP INDEX CREDNAME;

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Unique Indexes

When a column that is not the primary key requires unique values, create a unique index

A unique index is created by using the CREATE UNIQUE INDEX command

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Unique Indexes

Problem:Create a unique index named SSN on the

SOC_SEC_NUM column of the REP table

Solution:CREATE UNIQUE INDEX SSN ON

REP(SOC_SEC_NUM);

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System Catalog

Information about tables in the database is kept in the system catalog or the data dictionary

System catalog contains tables:SYSTABLES (in Oracle: DBA_TABLES)SYSCOLUMNS (in Oracle:

DBA_TAB_TABLES)SYSVIEWS (in Oracle: DBA_VIEWS)

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System Catalog

The system catalog is a relational database

Information can be retrieved by using the same types of queries which are used to retrieve data in a relational database

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System Catalog

The DBMS updates the system catalog automatically

Users should not use SQL queries to update the catalog directly because this might produce inconsistent information

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Integrity Rules in SQL

An integrity constraint is a rule for the data in the database

If a user enters data in the database that violates any of the integrity constraints, the database will develop serious problems

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Integrity Rules in SQL

Integrity support is the process of specifying integrity constraints for a database that the DBMS will enforce The types of constraints supported in SQL are:Primary keysForeign keysLegal values

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Integrity Rules in SQL

In most cases, a table’s primary key is indicated when the table is created

To add a primary key after creating a table, use the ADD PRIMARY KEY clause of the ALTER TABLE command

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Integrity Rules in SQL

A foreign key is a column in one table whose values match the primary key in another table

When a table contains a foreign key, it is identified by using the ADD FOREIGN KEY clause of the ALTER TABLE command

After creating a foreign key, the DBMS will reject any update that violates the foreign key constraint

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Integrity Rules in SQL

The CHECK clause of the ALTER TABLE command is used to ensure that only legal values satisfying a particular condition are allowed in a given column

If a user enters data that violates the condition, the DBMS rejects the update automatically

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Summary

A view contains data that is derived from existing base tables when users attempt to access the viewGRANT command: gives users access privileges to data in the databaseREVOKE command: terminates previously granted privileges You can create and use an index to make data retrieval more efficient

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Summary

The DBMS maintains information about the tables, columns, indexes, and other system elements in the system catalog (catalog) or data dictionary

Integrity constraints are rules that the data in the database must follow to ensure that only legal values are accepted in specified columns and that primary and foreign key values match between tables

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SQL Project Six Completed

Good Luck

H. Zamanzadeh