Contents
What is Cascade delete update?
CASCADE. It is used in conjunction with ON DELETE or ON UPDATE. It means that the child data is either deleted or updated when the parent data is deleted or updated. SET NULL. It is used in conjunction with ON DELETE or ON UPDATE.
What is on delete cascade?
Use the ON DELETE CASCADE option to specify whether you want rows deleted in a child table when corresponding rows are deleted in the parent table. If you do not specify cascading deletes, the default behavior of the database server prevents you from deleting data in a table if other tables reference it.
What is on update cascade in MySQL?
So, for example, adding the ON UPDATE CASCADE clause to a foreign key definition tells MySQL that when a record is updated in the primary table (the table referenced for foreign key checks), all records using that foreign key value in the current table should also be automatically updated with the new values to ensure …
How does on update cascade work?
ON UPDATE CASCADE means that if the parent primary key is changed, the child value will also change to reflect that.
What does on delete Cascade mean in MySQL?
ON DELETE CASCADE is an optional clause in a foreign key declaration. So it goes with the foreign key declaration. (Meaning, in the “child” table.) …it could mean delete the Parent record when the Child record is deleted, or it could mean delete the Child record when the Parent is deleted.
What’s the difference between delete Cascade and delete restrict?
0 votes. ON delete cascade: when a row in the parent table is deleted ,InnoDB will automatically delete corresponding foreign key columns in the child table. ON delete restrict: disallows a delete if an associated record still exists.
When to delete cascade in SQL Server foreign key?
DELETE CASCADE: When we create a foreign key using this option, it deletes the referencing rows in the child table when the referenced row is deleted in the parent table which has a primary key.
Which is Records trigger a cascade in MySQL?
For example, if I have two tables – Parent and Child – with a foreign key on Child that references Parent and has ON DELETE CASCADE, which records trigger a cascade and which records get deleted by the cascade?