Action upon Delete

Specifies what action is to take place on the dependent tables when a row of the parent table is deleted.

No Action
Specifies that the row in the parent table can be deleted if no other row depends on it. If a dependent row exists in the relationship, the DELETE fails. The check for dependent rows is performed at the end of the statement.

Restrict
Specifies that the row in the parent table can be deleted if no other row depends on it. If a dependent row exists in the relationship, the DELETE fails. The check for dependent rows is performed immediately.

Cascade
Specifies that first the designated rows in the parent table are deleted. Then, the dependent rows are deleted.

Set Null
Specifies that each nullable column of the foreign key in each dependent row is set to null. This means that the column is only set to null if it is a member of a foreign key that references the row being deleted. Only the dependent rows that are immediate descendants are affected.

Set Default
Specifies that each nullable column of the foreign key in each dependent row is set to its default value. This means that the column is only set to its default value if it is a member of a foreign key that references the row being deleted. Only the dependent rows that are immediate descendants are affected.