Adding and removing referential constraints

You can use the CREATE TABLE statement or the ALTER TABLE statement to add a referential constraint. To remove a referential constraint, use the ALTER TABLE statement.

Constraints are rules that ensure that references from one table, a dependent table, to data in another table, the parent table, are valid. You use referential constraints to ensure referential integrity.

With a referential constraint, non-null values of the foreign key are valid only if they also appear as values of a parent key. When you define a referential constraint, you specify:

A primary or unique key
A foreign key
Delete and update rules that specify the action taken with respect to dependent rows when the parent row is deleted or updated.

Optionally, you can specify a name for the constraint. If a name is not specified, one is automatically generated.

After a referential constraint is defined, the system enforces the constraint on every INSERT, DELETE, and UPDATE operation performed through SQL or any other interface, including System i® Navigator, CL commands, utilities, or high-level language statements.