Question

I have 2 tables, call A and B. A has a foreign key on B. call them A_ID and B_ID respectively. But the constraint not enforced in the design. I am not supposed to change the schema. I need to delete entries from table A based on 2 conditions.
1)If table B doesn’t contain A_ID
2)If some condition on B is met.

I have formed a query something like this. But I dont think its optimal. Is there a better way of doing this?

delete from A where A_ID not in (select B_ID from B where status='x' ) 
                 or A_ID not in (select B_ID from B)

Answer 1

You could use not exists to delete rows without a matching entry in table B. This one treats status = 'x' as if no match was found, i.e. it will delete those rows:

delete  A
where   not exists
        (
        select  *
        from    B
        where   B.B_ID = A.A_ID
                and status <> 'x'
        )