mysql数据库怎么去除重复数据

delete from zhszty_ebook

where id not in(

select * from (select max(id) from zhszty_ebook group by url

) as tmp)------------mysql有个特性，对于表进行修改，删除 *** 作，子查询不能和外层的查询的表一样，所以在加个select就可以了。其他数据库按照楼上的那个是没问题的

1. 查询需要删除的记录，会保留一条记录。

select a.id,a.subject,a.RECEIVER from test1 a left join (select c.subject,c.RECEIVER ,max(c.id) as bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having count(1) >1) b on a.id<b.bid where a.subject=b.subject and a.RECEIVER = b.RECEIVER and a.id <b.bid

2. 删除重复记录，只保留一条记录。注意，subject,RECEIVER 要索引，否则会很慢的。

delete a from test1 a, (select c.subject,c.RECEIVER ,max(c.id) as bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having count(1) >1) b where a.subject=b.subject and a.RECEIVER = b.RECEIVER and a.id <b.bid

---