Remove rows NOT referenced by a foreign key

Question

This is somewhat related to this question:

I have a table with a primary key, and I have several tables that reference that primary key (using foreign keys). I need to

Answer 1

DELETE
FROM    group g
WHERE   NOT EXISTS
        (
        SELECT  NULL
        FROM    table1 t1
        WHERE   t1.groupid = g.groupid
        UNION ALL
        SELECT  NULL
        FROM    table1 t2
        WHERE   t2.groupid = g.groupid
        UNION ALL
        …
        )