Sybase 12.4.2 manual SQL statements for implementing integrity constraints, 276

Data integrity overview

Entity and referential integrity

These and other table and column constraints are discussed in “Using table and column constraints”. Column constraints can be inherited from user-defined data types.

The information in relational database tables is tied together by the relations between tables. These relations are defined by the primary keys and foreign keys built into the database design. The following integrity rules define the structure of the database:

•Entity integrity Keeps track of the primary keys. It guarantees that every row of a given table can be uniquely identified by a primary key that guarantees no nulls. Adaptive Server IQ enforces single-column primary keys only; it does not enforce multi-column primary keys.

•Referential integrity Keeps track of the foreign keys that define the relationships between tables. All foreign key values either should match a value in the corresponding primary key or contain the NULL value if they are defined to allow NULL. Adaptive Server IQ does not enforce foreign keys, however.

For more information about referential integrity, see “Declaring entity and referential integrity”.

SQL statements for implementing integrity constraints

The following SQL statements are used to implement integrity constraints:

•CREATE TABLE statement This statement is used to implement integrity constraints as the database is being created.

•ALTER TABLE statement This statement is used to add integrity constraints, or to delete constraints, from an existing database.

For full descriptions of the syntax of these statements, see “SQL Statements” in Adaptive Server IQ Reference Manual.

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