mysql如何实现查重只留一个

概述mysql如何实现查重只留一个

@H_403_1@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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@H_403_1@MysqL 删除重复数据只保留一条记录

@H_403_1@删除重复数据保留name中ID最小的记录

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);

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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)

@H_403_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 *** 作之前应用；而 HAVING 搜索条件在进行分组 *** 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。)

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@H_403_1@扩展：

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@H_403_1@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

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@H_403_1@ 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

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

@H_403_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

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)

@H_403_1@3、查找表中多余的重复记录（多个字段）

select * from vitae a where (a.peopleID,a.seq) in (select peopleID,seq from vitae group by peopleID,seq having count(*) > 1)

@H_403_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

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)

@H_403_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

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)

@H_403_1@6.消除一个字段的左边的第一位：

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

@H_403_1@7.消除一个字段的右边的第一位：

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

@H_403_1@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

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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