mysql去重之实战总结

一、有主键去重

a、单字段重复

 

table  ab

查询重复记录(一条)

select aid from ab group by aid having count(*)>1

result:

  查询重复记录(全部)

select * from ab t where t.aid in(select aid from ab group by aid having count(*)>1);

result:

   删除重复记录保留一条

delete from ab where aid in(
　　select aid from ab group by aid having count(*)>1
)and id not in(
　　select max(id)as id from ab group by aid having count(*)>1
)

刚开始想到这个sql，结果

 于是经过查资料，sql整改

delete from ab where aid in(
    select t.aid from(
        select aid from ab group by aid having count(*)>1
    ) t
)and id not in(
    select t.id from(
        select max(id) as id from ab group by aid having count(*)>1
    ) t
)        

 

 去重成功！

 

  b、多字段重复

table  ab

 查询重复记录(一条)

select aid,bid from ab group by aid,bid having count(*)>1

result:

   查询重复记录(全部)

select * from ab t where(t.aid,t.bid)in(select aid,bid from ab group by aid,bid having count(*)>1);

result:

 删除重复记录保留一条

delete from ab where (aid,bid) in (
	select t.aid,t.bid from (
		select aid,bid from ab group by aid,bid having count(*)>1
	) t
) and id not in (
	select t.id from (
		select max(id) as id from ab group by aid,bid having count(*)>1
	) t
)

去重成功！

 

二、无主键去重

单字段、多字段

table ab

  删除重复记录保留一条

--建临时表插入去重数据
create table ab_temp (select * from ab group by aid,bid having count(*)>1);
--删除重复数据
delete from ab where (aid,bid) in (
	select t.aid,t.bid from (
		select aid,bid from ab group by aid,bid having count(*)>1
	) t 
);
--插入去重数据
insert into ab select * from ab_temp;
--删除临时表
drop table ab_temp;

 去重成功！