mysql對表中數據根據某一字段去重

要刪除重復的記錄，就要先查出重復的記錄，這個很容易做到

select * from 表名 group by 根據哪一個字段（簡稱字段） having count(字段) > 1

注意：這是查出所有重復記錄的第一條記錄，需要保留，因此需要添加查詢條件，查出所有的重復記錄

select id,expect from cqssc where expect in (select expect from cqssc group by expect having count(expect)>1) 

and id not in(select min(id) from cqssc group by expect having count(expect)>1)

 

然后

delete from cqssc where id in (select id from (select id from cqssc where expect in 

(select expect from cqssc group by expect having count(expect)>1) and id not in

(select min(id) from cqssc group by expect having count(expect)>1)) as tmpresult)

刪除成功，最后再查詢一下看是否還有重復記錄