mysql基础2【常用mysql语句】-优快云博客

本文链接：https://blog.youkuaiyun.com/lixld/article/details/46486709

本文提供了一套实用的SQL语句，用于查找和删除数据库表中的重复记录，支持单字段及多字段的重复记录处理，并提供了存储过程示例。

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常用的语句

1、查找表中多余的重复记录，重复记录是根据单个字段（mail_id）来判断

代码如下	复制代码
SELECT * FROM table WHERE mail_id IN (SELECT mail_id FROM table GROUP BY mail_id HAVING COUNT(mail_id) > 1);

2、删除表中多余的重复记录，重复记录是根据单个字段（mail_id）来判断，只留有rowid最小的记录

代码如下	复制代码
DELETE FROM table WHERE mail_id IN (SELECT mail_id FROM table GROUP BY mail_id HAVING COUNT(mail_id) > 1) AND rowid NOT IN (SELECT MIN(rowid) FROM table GROUP BY mail_id HAVING COUNT(mail_id )>1);

3、查找表中多余的重复记录（多个字段）

代码如下	复制代码
SELECT * FROM table WHERE (mail_id,phone) IN (SELECT mail_id,phone FROM table GROUP BY mail_id,phone HAVING COUNT(*) > 1);

4、删除表中多余的重复记录（多个字段），只留有rowid最小的记录

代码如下	复制代码
DELETE FROM table WHERE (mail_id,phone) IN (SELECT mail_id,phone FROM table GROUP BY mail_id,phone HAVING COUNT() > 1) AND rowid NOT IN (SELECT MIN(rowid) FROM table GROUP BY mail_id,phone HAVING COUNT()>1);

5、查找表中多余的重复记录（多个字段），不包含rowid最小的记录

代码如下	复制代码
SELECT * FROM table WHERE (a.mail_id,a.phone) IN (SELECT mail_id,phone FROM table GROUP BY mail_id,phone HAVING COUNT() > 1) AND rowid NOT IN (SELECT MIN(rowid) FROM table GROUP BY mail_id,phone HAVING COUNT()>1);

存储过程

代码如下

复制代码

declare @max integer,@id integer

declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >； 1

open cur_rows

fetch cur_rows into @id,@max

while @@fetch_status=0

begin

select @max = @max -1

set rowcount @max

delete from 表名 where 主字段 = @id