Overview of Referential Integrity (Visual Database Tools)

Procedure

You can set referential integrity when all of the following conditions are met:

• The matching column from the primary table is a primary key or has a unique constraint.

• The related columns in the foreign table have the same data type and size.

When referential integrity is enforced, you must observe the following rules:

• You cannot enter a value in the foreign-key column of the related table if that value does not exist in the primary key of the related table. However, you can enter a null in the foreign-key column. For example, you cannot indicate that a job is assigned to an employee who is not included in the employee table, but you can indicate that an employee has no assigned job by entering a null in the job_id column of the employee table.

• You cannot delete a row from a primary key table if rows matching it exist in a related table. For example, you cannot delete a row from the jobs table if there are employees assigned to the job represented by that row in the employee table.

• You cannot change a primary key value in the primary key table if that row has related rows. For example, you cannot change a row's job_id value in the jobs table if there are employees with that job_id in the employee table.

See Also

Reference

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