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

SELECT num, MAX(date) AS date FROM A GROUP BY num

大家在这里回答问题纯粹就是助人为乐，度娘的分值咩用都木。没有老土的SQL，只有没有经验的数据库初学者，说这么多，直接看VIEW是通过哪些表创建的，直接在这些表里面group by不就行了。 Mysql 这么高效的SQL不用，非要来回绕圈子找些古怪的法子，这不是技术高明，这是退而求其末

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

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