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Chapter 6Database Administration

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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 (SQL command that indicates the rows and columns that will appear in the view)

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Creating the HOUSEWARES View

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HOUSEWARES View

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Views

Data does not exist in the form of the view

Query acts as a “window” into the database (see Figure 6.3)

As far as the user is concerned the entire database consists of the dark shaded portion of the PART table

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Using the HOUSEWARES View

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Using the HOUSEWARES View

In Figure 6.4, the query first is merged with the query that defines the view, producing the following statement:

SELECT PART_NUMBER, PART_DESCRIPTION, UNITS_ON_HAND, UNIT_PRICE

FROM PART

WHERE ITEM_CLASS = ‘HW’

AND UNITS_ON_HAND > 100;

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CREATE VIEW Format

The formulation of the view definition is: CREATE <view name> AS <query>

The defining query can be any valid SQL query

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Renaming Columns When Creating a View

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View Benefits

Views provide data independence

Different users can view the same data in different ways because each user has their own view

It can contain only those columns required by a given user Greatly simplifies user perception of database Furnishes a measure of security since user as

access to data contained only in their view

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Row-and-Column Subsets and Updates through a ViewA 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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Creating the SALES_CRED View

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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

Views involving statistics calculated from one or more base tables won’t allow updatesRows cannot be added to a view that

includes calculations

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Dropping a View

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DROP View Command

Deletes a view definition only

Table and data on which view is based still exists

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Security

Security is the prevention of unauthorized access to the database

Two security mechanismsViewsGRANT command

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GRANT and REVOKE Commands

Grant different privileges to users and revoke them later, if necessary:Ability to select rows from a table Insert new rowsUpdate existing rows

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Example 6

User Jones must be able to retrieve data from the SALES_REP tableGRANT SELECT ON SALES_REP TO

JONES;

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Privileges

Privileges that can be granted are SELECT UPDATE DELETE INSERT INDEX

For a user to pass the privilege on to others the database administrator must use GRANT statement and include WITH GRANT OPTION

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GRANT and REVOKE Format

GRANT <privilege> TO <user>

REVOKE <privilege> FROM <user>WITH GRANT OPTION is not meaningful

part of REVOKE commandRevoke cascades so privileges granted

with the WITH GRANT OPTION are revoked for all who were granted privileges

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Example 14

User Jones is no longer allowed to retrieve data from the SALES_REP tableREVOKE SELECT ON SALES_REP

FROM JONES;

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Indexes

Create and use an index to speed the searching process

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Index for CUSTOMER Table on CUSTOMER_NUMBER Column

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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 Indexes

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Dropping an Index

Command to delete an index is DROP INDEXDROP INDEX CREDNAME;

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Unique Indexes

When a column that is not the primary key requires unique values, create a unique index using the CREATE UNIQUE INDEX commandCREATE UNIQUE INDEX SSN ON

CUSTOMER (SOC_SEC_NUMBER);

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The System Catalog

Information concerning tables known to the DBMS is kept in the system catalog, or the data dictionary

System catalog contains tablesSYSTABLES (in Oracle: DBA_TABLES)SYSCOLUMNS (in Oracle:

DBA_TAB_TABLES)SYSVIEWS (in Oracle: DBA_VIEWS)

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System Catalog

System catalog is a relational database

Users need special privileges to view the data in the system catalog

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Tables Owned by PRATT

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Integrity in SQL

An integrity constraint is a rule that the data in the database must follow

Examples: No two sales reps can have the same sales rep

number The sales rep number for a customer must match

the number of a sales rep currently in the database

Item classes for parts must be AP, HW, or SG

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Integrity Support

To prevent violations, the DBMS provides integrity supportTypes of constraints supported in SQL Legal values Primary keys Foreign keys

CHECK clause ensures that only legal values that satisfy a particular condition are allowed in a given column

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CHECK Clause

To ensure the only legal values for item class are AP, HW, or SGCHECK (ITEM_CLASS IN (‘AP’, ‘HW’,

‘SG’))

ORCHECK (ITEM_CLASS = ‘AP’ OR

ITEM_CLASS = ‘HW’ OR ITEM_CLASS = ‘SG’)

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ADD PRIMARY KEY Clause

To indicate that SLSREP_NUMBER is the primary key for the SALES_REP tablePRIMARY KEY (SLSREP_NUMBER)

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Foreign Key

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

To specify a foreign key, specify both the column that is a foreign key and the table it matchesADD FOREIGN KEY (SLSREP_NUMBER)

REFERENCES SALES_REP

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Assigning a Primary Key

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Adding Foreign Keys