MySql資料查重、去重的實現
假設有一個表user,欄位分別有id–nick_name–password–email–phone,分情況如下(注意刪除多餘記錄時要建立臨時表,不然會報錯):
一、單欄位(nick_name)
1、查出所有有重複記錄的所有記錄
select * from user where nick_name in (select nick_name from user group by nick_name having count(nick_name)>1); 1 2 3 2、查出有重複記錄的各個記錄組中id最大的記錄
select * from user where id in (select max(id) from user group by nick_name having count(nick_name)>1); 1 3、查出多餘的記錄,不查出id最小的記錄
select * from user where nick_name in
(select nick_name from user group by nick_name having count(nick_name)>1)
and id not in
(select min(id) from user group by nick_name having count(nick_name)>1); 1 2 3 4 5 6 7 4、刪除多餘的重複記錄,只保留id最小的記錄
delete from user where nick_name in (select nick_name from
(select nick_name from user group by nick_name having count(nick_name)>1) as tmp1)
and id not in
(select id from
(select min(id) from user group by nick_name having count(nick_name)>1) as tmp2); 1 2 3 4 5 6 7 8 9 10 11 二、多欄位(nick_name,password)
1、查出所有有重複記錄的記錄
select * from user where (nick_name,password) in
(select nick_name,password from user group by nick_name,password where having count(nick_name)>1); 1 2 3 2、查出有重複記錄的各個記錄組中id最大的記錄
select * from user where id in
(select max(id) from user group by nick_name,password where having count(nick_name)>1); 1 2 3 3、查出各個重複記錄組中多餘的記錄資料,不查出id最小的一條
select * from user where (nick_name,password) in
(select nick_name,password from user group by nick_name,password having count(nick_name)>1)
and id not in
(select min(id) from user group by nick_name,password having count(nick_name)>1); 1 2 3 4 5 6 7 4、刪除多餘的重複記錄,只保留id最小的記錄
delete from user where (nick_name,password) in
(select nick_name,password from
(select nick_name,password from user group by nick_name,password having count(nick_name)>1) as tmp1)
and id not in
(select id from
(select min(id) id from user group by nick_name,password having count(nick_name)>1) as tmp2);