【mysql】sql刪除多個欄位重複資料有主鍵和沒主鍵解決方法
table user
name age nub
張三 12 23
張三 12 23
張三 12 23
李四 13 21
李四 13 21
王五 11 25
查詢重複記錄(一條)
sql:select * from user group by name,age,nub having count(*)>1;
(如需統計條數請使用conut)
set:
name age nub
張三 12 23
李四 13 21
查詢重複記錄(所有)
sql:select * from user a where (a.name,a.age,a.nub) in (select * from user group by name,age,nub having count(*)>1);
set
name age nub
張三 12 23
張三 12 23
張三 12 23
李四 13 21
李四 13 21
刪除重複記錄保留一條
步驟:
1.將查詢的資料插入一個新的表中;
2.刪除原來的表的資料
3.將新表的資料再插入原表中
4,刪除新表
sql:
1. create table new_table (select * from user group by name,age,nub having count(*)>1);
2.delete from user a where (a.name,a.age,a.nub) in
(select * from
(select * from user group by name,age,nub having count(*)>1) as b );
在這裡使用了兩次select 因為:
delete from user a where (a.name,a.age,a.nub) in
(select * from user group by name,age,nub having count(*)>1);會出現錯誤
不能對同一表子查詢後進行插入或者刪除 要在子查詢再巢狀一個查詢 讓對該表查詢成為孫查詢;
注:這裡更正一下,我按照上面的無法執行,要去除a才可以,如下:
delete from user where (name,age,nub) in
(select * from
(select * from user group by name,age,nub having count(*)>1) as b );
3.insert into user (select name,age,nub from new_table);
注意:在插入資料的時候查詢表得到欄位的順序要與原表相同否者會出現資料錯誤;
如果原表資料順序與新表相同可以用這條語句insert into user (select * from new_table);
4.drop table new_table;
到此完成操作 最後的資料:
table user
name age nub
張三 12 23
李四 13 21
王五 11 25
如果原表中含有主鍵的話更好操作
不用四條sql語句了 直接執行刪除操作
delete from user a where (a.name,a.age,a.nub) in
(select name,age,nub from
(select * from user group by name,age,nub having count(*)>1) as b )
and id not in(select min(id) from
(select * from user group by name,age,nub having count(*)>1) as c);
注意事項: 在使用 (name,age,address) in (select *)的時候 * 只能是三列 如果有更多列則
不能使用 *,要明確指出是哪些列;