mysql如何实现查重只留一个-木庄网络博客

本文摘自PHP中文网，作者藏色散人，侵删。

mysql实现查重只留一个的方法：首先通过“select * from”查找表中多余的重复记录；然后通过“delete from”删除重复数据，并只保留一个数据即可。

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mysql 删除重复数据只保留一条记录

删除重复数据保留name中id最小的记录

1	`delete` `from order_info where id not in (select id from (select min(id)` `as` `id from order_info group by order_number)` `as` `b);`

1	`delete` `from table where id not in (select min(id) from table group by name having` `count(name)>1)` `and` `id in (select id group by name having` `count(name)>1)`

(注意：HAVING 子句对 GROUP BY 子句设置条件的方式与 WHERE 和 SELECT 的交互方式类似。WHERE 搜索条件在进行分组操作之前应用；而 HAVING 搜索条件在进行分组操作之后应用。HAVING 语法与 WHERE 语法类似，但 HAVING 可以包含聚合函数。HAVING 子句可以引用选择列表中显示的任意项。)

扩展：

SQL：删除重复数据，只保留一条用SQL语句,删除掉重复项只保留一条在几千条记录里,存在着些相同的记录,如何能用SQL语句,删除掉重复的呢

1、查找表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断

1	`select * from people where peopleId in (select peopleId from people group by peopleId having` `count(peopleId) > 1)`

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

1	`delete` `from people where peopleName in (select peopleName from people group by peopleName having` `count(peopleName) > 1)` `and` `peopleId not in (select min(peopleId) from people group by peopleName having` `count(peopleName)>1)`

3、查找表中多余的重复记录（多个字段）

1	`select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq 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

1	`delete` `from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having` `count() > 1)` `and` `rowid not in (select min(rowid) from vitae group by peopleId,seq 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

1	`select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having` `count() > 1)` `and` `rowid not in (select min(rowid) from vitae group by peopleId,seq having` `count()>1)`

6.消除一个字段的左边的第一位：

1	`update tableName set [Title]=Right([Title],(len([Title])-1)) where Title like` `'村%'`

7.消除一个字段的右边的第一位：

1	`update tableName set [Title]=left([Title],(len([Title])-1)) where Title like` `'%村'`

8.假删除表中多余的重复记录（多个字段），不包含rowid最小的记录

1	`update vitae set ispass=-1 where peopleId in (select peopleId from vitae group by peopleId,seq having` `count() > 1)` `and` `seq in （select seq from vitae group by peopleId,seq having` `count() > 1）` `and` `rowid not in (select min(rowid) from vitae group by peopleId,seq having` `count(*)>1)`

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