mysql如何实现查重只留一个

藏色散人
发布: 2020-11-01 14:33:16
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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。

mysql如何实现查重只留一个

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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

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)
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(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

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