mysql去重之實戰總結

1、有主鍵去重

a、單字段重複

 

table  ab

查詢重複記錄(一條)

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

result:

  查詢重複記錄(所有)

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

result:

   刪除重複記錄保留一條

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
)

剛開始想到這個sql，結果

 因而通過查資料，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、多字段重複

table  ab

 查詢重複記錄(一條)

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

result:

   查詢重複記錄(所有)

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

result:

 刪除重複記錄保留一條

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！

 

2、無主鍵去重

單字段、多字段

table ab

  刪除重複記錄保留一條

--建臨時表插入去重數據
create table ab_temp (select * from ab group by aid,bid having count(*)>1);
--刪除重複數據
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 
);
--插入去重數據
insert into ab select * from ab_temp;
--刪除臨時表
drop table ab_temp;

 去重成功！