删除重复记录，并保留一条记录

DELETE from tiaoyaxiang_bk
 WHERE tyx_id IN (SELECT tyx_id FROM tiaoyaxiang_bk GROUP BY tyx_id HAVING COUNT(tyx_id) > 1)
   AND ROWID NOT IN
       (SELECT MIN(ROWID) FROM tiaoyaxiang_bk GROUP BY tyx_id HAVING COUNT(*) > 1);