Question

Looking for query, remove all record of child table where parent id not match with master record.

Master-Table

 1. David
 2. Fin
 3. Lisa

Child-Table

 1. 100
 1. 200
 2. 200
 2. 222
 8. 100
 9. 100

Output Required on Child Table

 1. 100
 1. 200
 2. 200
 2. 222

want to remove record # 8 and 9 from child table, cuz it doesn’t have parent id.

Thanks

Answer 1

You can use an outer join in a DELETE operation:

DELETE a 
FROM child a
LEFT JOIN master b ON a.parent_id = b.id
WHERE b.id IS NULL

To prevent the need to do this, what you should look into are Referential CASCADE actions that execute whenever you delete a parent (row in the master table).

If you have an ON DELETE CASCADE set up on the foreign key in your child table, any parent that gets deleted will also have all of its corresponding “children” deleted as well.