Action ON UPDATE
The ONE UPDATE Action specifies what should happen with child records when you UPDATE the PRIMARY KEY of a parent record. With help of this you can control Referential Integrity of your database, thereby enforcing business rules at the database level.
When you are going to UPDATE the PK of the parent record this raise question: what should happens with value of PTR field of its child records? The answer gives the ON UPDATE Action of a Link.
You can specify one of the following constants:
- RESTRICT - default, means that UPDATE of PK field of the parent record is refused if at least one child record exists. NO ACTION is synonym of RESTRICT.
- CASCADE - means that value of PTR field is set to the same value of PK, i.e. child records still point the same parent record.
- SET NULL - means that value of PTR field is set to NULL, i.e. child record(s) still exist(s) but do not have parent record.
- SET DEFAULT - means that value of PTR field is set to its default value, i.e. it looks like a child record gets a new parent record.