MySQL删除重复数据行，只保留一条
delete from devices_allwhere device_id in (select device_id from (select device_id from devices_all a group by a.device_id having count(a.device_id) > 1) as a) and device_all_id not in (select device_all_id from (select min( device_all_id) device_all_id from devices_all group by device_id having count( device_id)>1) as b)

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