Which are three delete rules for referential integrity constraints?

The delete rule of a referential constraint is specified when the referential constraint is defined. The choices are NO ACTION, RESTRICT, CASCADE, or SET NULL.

What is on update restrict?

RESTRICT allows you to delete data referred to by a foreign key only if no other data relies on it. e.g. deleting a customer record when there are customer orders referring to it. A customer who has made no orders could be safely deleted.

What is the purpose of cascade and restrict?

Restrict and Cascade. Deletes all objects that depend on the dropped constraint or column. For example, if a unique constraint upon which a referential constraint is dependent is dropped, the dependent constraints are dropped.

Is restrict a delete rule?

RESTRICT : Rejects the delete or update operation for the parent table. Specifying RESTRICT (or NO ACTION ) is the same as omitting the ON DELETE or ON UPDATE clause.

Is on delete restrict default?

NO ACTION and RESTRICT do the same thing (prevent any DB change that breaks an FK) and that thing is the default so if you omit an ON DELETE clause you’re saying NO ACTION (or RESTRICT — same thing).

What is the difference between on delete cascade and on delete set null?

Set NULL : Sets the column value to NULL when you delete the parent table row. CASCADE : CASCADE will propagate the change when the parent changes. If you delete a row, rows in constrained tables that reference that row will also be deleted, etc.

What is on delete cascade and on delete set null?

Referential actions include:

1. CASCADE : Delete or update the row from the parent table and automatically delete or update the matching rows in the child table.
2. SET NULL : Delete or update the row from the parent table and set the foreign key column or columns in the child table to NULL .

What does on delete restrict mean?

ON DELETE RESTRICT means you can’t delete a given parent row if a child row exists that references the value for that parent row. If the parent row has no referencing child rows, then you can delete that parent row. ON DELETE RESTRICT is pretty much superfluous syntax, because this is the default behavior for a foreign key anyway.

What is Onon delete restrict in SQL Server?

ON DELETE RESTRICT means you can’t delete a given parent row if a child row exists that references the value for that parent row. If the parent row has no referencing child rows, then you can delete that parent row.

What is the difference between restrestriction and enforcement?

Restriction: After you define informational constraints on a table, you can alter the column names only for that table after you remove the informational constraints. ENFORCED or NOT ENFORCED: Specifies whether the constraint is enforced by the database manager during normal operations such as insert, update, or delete.

Where is the restrict keyword in Oracle?

In Oracle, there is no RESTRICT keyword. The only option is NO ACTION. In MySQL, there is no difference between ON DELETE RESTRICT and ON DELETE NO ACTION. If There Is a Difference Though…