ASA SQL User's Guide
Ensuring Data Integrity
Enforcing entity and referential integrity
Once you specify the primary key for each table, maintaining entity integrity requires no further action by either client application developers or by the database administrator.
The table owner defines the primary key for a table when they create it. If they modify the structure of a table at a later date, they can also redefine the primary key.
Some application development systems and database design tools allow you to create and alter database tables. If you are using such a system, you may not have to enter the CREATE TABLE or ALTER TABLE statement explicitly: the application may generate the statement itself from the information you provide.
For more information about creating primary keys, see Managing primary keys. For the detailed syntax of the CREATE TABLE statement, see CREATE TABLE statement. For information about changing table structure, see the ALTER TABLE statement.