Mysql - 删除具有重复列的行[重复]答案

【问题标题】：Mysql - Delete rows with duplicate columns [duplicate]Mysql - 删除具有重复列的行[重复]
【发布时间】：2015-05-25 15:35:54
【问题描述】：

此查询返回重复列 col B、col C、col D 的计数

SELECT `colB`, `colC`, `colD`, COUNT(1) as CNT
FROM `table`
GROUP BY `colB`, `colC`, `colD` 
HAVING COUNT(1) > 1

如何在保留一条的同时删除重复的记录？

DELETE FROM `table` WHERE  ( 
// Keep one record and delete rows with duplicate columns b,c,d 
)

colA 是主键 - AI

【问题讨论】：

标签： sql

【解决方案1】：

如果你有主键，你可以这样做：

delete t
   from table t left join
        (select cola, colb, colc, min(cola) as cola
         from table t
         group by cola, colb, colc
        ) tokeep
        on t.cola = tokeep.cola
    where tokeep.cola is null;

但是，对表进行大量删除可能效率低下。因此，将数据移动到临时表并重新插入通常会更快：

create temporary table tokeep as
    select min(cola) as cola, colb, colc, cold
    from table t
    group by colb, colc, cold

truncate table `table`;

insert into `table`(cola, colb, colc, cold)
    select cola, colb, colc, cold
    from tokeep;

【讨论】：

【解决方案2】：

试试这个

DELETE  a
FROM    table a
        LEFT JOIN
        (
            SELECT MIN(colA) colA , colB , colC ,colD 
            FROM    Table
            GROUP   BY colB , colC,colD  
        ) b ON  a.colA = b.colA and a.colB = b.colB and a.colC = b.colC and a.colD = b.colD
WHERE   b.colA IS NULL

【讨论】：

【解决方案3】：

尝试类似：

DELETE t1 
FROM table t1 INNER JOIN table t2 
ON t1.colB = t2.ColB 
AND t1.colC = t2.ColC 
AND t1.colD = t2.ColD
AND t1.colA > t2.ColA

【讨论】：