sql查出重复数据，删除重复数据只留一条（小白专用）
查表中多余重复记录，根据单个字段（username）来判断
select username,count() as num from tusertest group by username having COUNT()>1
删除重复
DELETE FROM tusertest WHERE id NOT IN
(SELECT MIN(id) FROM tusertest
GROUP BY username);
查表中多余重复记录，根据单个字段（username）来判断
select username,count() as num from tusertest group by username having COUNT()>1
删除重复
DELETE FROM tusertest WHERE id NOT IN
(SELECT MIN(id) FROM tusertest
GROUP BY username);