刪除mysql中的重複記錄只保留一條語句

DELETE FROM device_info WHERE mac IN (
       SELECT * FROM ( 
               SELECT mac from device_info GROUP BY mac HAVING count(mac) > 1) q) 
   AND id NOT IN ( 
       SELECT * FROM (
               SELECT MIN(id) FROM device_info GROUP BY mac HAVING count(mac) > 1) r)

刪除字段：mac重複的記錄，保留id最小的記錄