Delete duplicate rows from small table

A faster solution is

DELETE FROM dups a USING (
      SELECT MIN(ctid) as ctid, key
        FROM dups 
        GROUP BY key HAVING COUNT(*) > 1
      ) b
      WHERE a.key = b.key 
      AND a.ctid <> b.ctid

This is fast and concise:

DELETE FROM dupes T1
    USING   dupes T2
WHERE   T1.ctid < T2.ctid  -- delete the older versions
    AND T1.key  = T2.key;  -- add more columns if needed

See also my answer at How to delete duplicate rows without unique identifier which includes more information.

DELETE FROM dupes a
WHERE a.ctid <> (SELECT min(b.ctid)
                 FROM   dupes b
                 WHERE  a.key = b.key);