mysql查询与删除重复记录多种方法

发布时间:2020-01-28编辑:脚本学堂
本文介绍了mysql查询与删除重复记录的方法,以及mysql删除重复记录的一些sql语句,有需要的朋友参考下。

 mysql如何查询与删除重复记录

方法一:
 

复制代码 代码示例:
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
fetch cur_rows into @id,@max
end
close cur_rows
set rowcount 0

方法二:有两个意义上的重复记录,一是完全重复的记录,也即所有字段均重复的记录,二是部分关键字段重复的记录,比如Name字段重复,而其他字段不一定重复或都重复可以忽略。
1、对于第一种重复,比较容易解决,使用:
 

复制代码 代码示例:
select distinct * from tableName

就可以得到无重复记录的结果集。
如果该表需要删除重复的记录(重复记录保留1条),可以按以下方法删除
 

复制代码 代码示例:
select distinct * into #Tmp from tableName
drop table tableName
select * into tableName from #Tmp
drop table #Tmp
 

发生这种重复的原因是表设计不周产生的,增加唯一索引列即可解决。

2、这类重复问题通常要求保留重复记录中的第一条记录,操作方法如下
假设有重复的字段为Name,Address,要求得到这两个字段唯一的结果集
 

复制代码 代码示例:
select identity(int,1,1) as autoID, * into #Tmp from tableName
select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID
select * from #Tmp where autoID in(select autoID from #tmp2)
 

最后一个select即得到了Name,Address不重复的结果集(但多了一个autoID字段,实际写时可以写在select子句中省去此列)

3、查询重复记录
 

复制代码 代码示例:
select * from tablename where id in (
select id from tablename
group by id
having count(id) > 1
)

附,mysql查询重复记录的方法。

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
 

复制代码 代码示例:
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
 

复制代码 代码示例:
delete from people
where peopleId  in (select  peopleId  from people  group  by  peopleId   having  count(peopleId) > 1)
and rowid not in (select min(rowid) from  people  group by peopleId  having count(peopleId )>1)

3、查找表中多余的重复记录(多个字段)
 

复制代码 代码示例:
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
 

复制代码 代码示例:
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
 

复制代码 代码示例:
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)