Books for you

Figure 1-2. Relational model with two tables
EMPNO
71712
83321
85332
88888
EMPNAME
Johnson
Smith
Stern
Carter
TITLE
Clerk
Mgr
SC Mgr
Mgr
DEPTNO
10
20
30
10
DEPTNO DEPTNAME LOCATION
10
20
30
40
Accounting
Research
Sales
Operations
San Francisco
San Francisco
Chicago
Dallas
The Evolution of the Relational Database | 5
Sequences
Provide unique numbers for column values.
Stored procedures
Contain logical modules that can be called from programs.
Synonyms
Provide alternative names for database objects.
Indexes
Provide faster access to table rows.
Database links
Provide links between distributed databases.
The relationships between columns in different tables are typically described through
the use of keys, which are implemented through referential integrity constraints and
their supporting indexes. For example, in Figure 1-2, you can establish a link
between the DEPTNO column in the second table, which is called a foreign key, to
the DEPTNO column in the first table, which is referred to as the primary key of that
table.


Pages:
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45