Clean up duplicate rows in a PostgreSQL table with differing IDs

gistfile1.txt

-- Expensive sub-query method:

delete from questions_tags qt using questions_tags qt2 where qt.question_id = qt2.question_id and qt.tag_id = qt2.tag_id and qt.id != qt2.id and qt.id not in (select min(id) from questions_tags qt3 where qt.question_id = qt3.question_id and qt.tag_id = qt3.tag_id);