What does on delete No action do?
The ON DELETE SET NULL action allows data that references the parent key to be deleted, but not updated. When referenced data in the parent key is deleted, all rows in the child table that depend on those parent key values have their foreign keys set to null.
What is on delete No action SQL?
ON DELETE NO ACTION : SQL Server raises an error and rolls back the delete action on the row in the parent table. ON DELETE CASCADE : SQL Server deletes the rows in the child table that is corresponding to the row deleted from the parent table.
Is on delete No action default?
The default is NO ACTION. So, you can elide ON DELETE NO ACTION if you like and it will work just the same. NO ACTION means that nothing will happen when you delete from your Subject table to the Topic table.
What is on delete Set null?
A foreign key with “set null on delete” means that if a record in the parent table is deleted, then the corresponding records in the child table will have the foreign key fields set to NULL. The records in the child table will not be deleted in SQL Server.
When to use on delete restrict?
When do we use ON DELETE RESTRICT? Whenever we don’t want “orphan” rows in the database! We don’t want to delete a customer from the CUSTOMER table if there are any orders for that customer in the ORDERS table.
How do you use Restrict on delete?
DELETE RESTRICT protects the parent from deletion, not the children. If you are wanting to delete the parent and leave the child, then you’re probably wanting the ON DELETE SET NULL option: 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 is on delete restrict?
The ON DELETE clause says that if a particular primary key ID value in the CUSTOMERS table is deleted, this action shall be prevented (this is the “restrict” part) if there is any row in the ORDERS table which has a foreign key that matches the value of the CUSTOMER table ID value.
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 restrict delete in access?
Restrict Delete – this option means that if you attempt to delete a record from one table but there is a corresponding record in the other table, the delete operation is not allowed.
What is difference between restrict and Cascade?
restrict: prevents the action from happening if there is any foreign keys that rely on the fields being changed i.e. modifies the behaviour of the master table. cascade: propagate the change when parent change i.e. modifies the behaviour of the child table.
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.
Why use restrict delete?
