Contents
When cascade delete is enabled in a relationship it causes?
Cascading deletes are needed when a dependent/child entity can no longer be associated with its current principal/parent. This can happen because the principal/parent is deleted, or it can happen when the principal/parent still exists but the dependent/child is no longer associated with it.
What is on delete cascade and on delete Set default?
ON DELETE CASCADE : SQL Server deletes the rows in the child table that is corresponding to the row deleted from the parent table. ON DELETE SET DEFAULT SQL Server sets the rows in the child table to their default values if the corresponding rows in the parent table are deleted.
What is on update no action?
In the case of a dependent row, the NO ACTION update rule is implicit when a foreign key is specified. NO ACTION means that a non-null update value of a foreign key must match some value of the parent key of the parent table when the update statement is completed.
What is on Delete no action?
NO ACTION means that nothing will happen when you delete from your Subject table to the Topic table. In that case, if there is a row in Topic for a given SubjectId you cannot delete from it without breaking referential integrity, so the Delete will be rolled back.
What does Cascade delete mean?
Cascade Delete. Cascade delete is commonly used in database terminology to describe a characteristic that allows the deletion of a row to automatically trigger the deletion of related rows.
What does on delete Cascade imply?
ON CASCADE DELETE means that all depending rows are deleted when the parent row is deleted. The parent row is in your dbo.Models table. Thus when you delete a record in Devices no record in Models is deleted.
What is Cascade delete related fields?
Simply so, what is Cascade delete related fields in Access? Cascade Delete – this option means that if you delete a record from one table, corresponding records in the other table are also deleted. 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 a cascade constraint?
The CASCADE CONSTRAINTS clause drops all referencial integrity constraints that refer to the primary and unique keys defined on the dropped columns.