WechatIMG256.jpeg

场景

在许多条记录里，存在着些相同的记录，使用SQL语句，删除掉重复项只保留一条。

数据模型

• half_demon 半妖表

单字段示例

• 查询语句

SELECT
    id,name 
FROM
    half_demon 
WHERE
    name IN ( SELECT name FROM half_demon GROUP BY name HAVING count( name ) > 1 )

查找表中多余的重复记录，重复记录是根据单个字段name来判断。

• 查询结果

• 删除语句

DELETE 
FROM
    half_demon 
WHERE
    id NOT IN ( SELECT hd.minid FROM ( SELECT MIN( id ) AS minid FROM half_demon GROUP BY name ) hd )

删除表中多余的重复记录，重复记录是根据单个字段name来判断，只留有id最小的记录。

• 删除结果

多字段示例

• 查询语句

SELECT
    id,
    name,
    weapon 
FROM
    half_demon a 
WHERE
    ( a.name, a.weapon ) IN ( SELECT name, weapon FROM half_demon GROUP BY name, weapon HAVING count( * ) > 1 )

查找表中多余的重复记录，重复记录是根据多个字段name、weapon来判断。

• 查询结果

• 删除语句

DELETE 
FROM
    half_demon 
WHERE
    ( name, weapon ) IN (
SELECT
    t.name,
    t.weapon 
FROM
    ( SELECT name, weapon FROM half_demon GROUP BY name, weapon HAVING count( 1 ) > 1 ) t 
    ) 
    AND id NOT IN ( SELECT hd.minid FROM ( SELECT min( id ) AS minid FROM half_demon GROUP BY name, weapon HAVING count( 1 ) > 1 ) hd )

删除表中多余的重复记录，重复记录是根据多个字段name、weapon来判断，只留有id最小的记录。

• 删除结果