Databases Reference
In-Depth Information
Sequences
Provide unique numbers, typically used 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.
Finally, even if you define many different indexes for a table, you don't have to under‐
stand them or manage the data they contain. Relational databases include a
query op‐
timizer
that chooses whether to use indexes, and the best way to use those indexes, to
access the data for any particular query.
The relational approach lent itself to the Structured Query Language (SQL). SQL was
initially defined over a period of years by IBM Research, but it was Oracle Corporation
that first introduced it to the market in 1979. SQL was noteworthy at the time for being
the only language needed for relational databases since you could use SQL:
• For queries (using a SELECT statement)
• As a Data Manipulation Language or DML (using INSERT, UPDATE, and DELETE
statements)
• As a Data Definition Language or DDL (using CREATE or DROP statements when
adding or deleting tables)
• To set privileges for users or groups (using GRANT or REVOKE statements)
Today, SQL contains many extensions and follows ANSI/ISO standards that define its
basic syntax.
How Oracle Grew
In 1983, Relational Software Incorporated was renamed Oracle Corporation to avoid
confusion with a competitor named Relational Technologies Incorporated. At this time,
the developers made a critical decision to create a portable version of Oracle written in
