MySQL查询及删除重复记录的方法

MySQL查询及删除重复记录的方法

2009-07-31 17:03

查询及删除重复记录的方法

(一)
一、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)

二、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 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)

三、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)

四、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) 执行报错

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

 

sed -e 's|\|||g'  -e '/+/d'  -e 's|\ ||g'   txt > txt2

删除脚本：

#!/bin/bash

cat txt2|while read line
do
echo "delete from monitor_sub_task where id=$line;">> ./sql/delete.sql
donecat txt3|while read line;do mysql -uroot  boss_monitor -e "delete from monitor_sub_task where id=$line;";done

五、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)

(二)
比方说
在A表中存在一个字段“name”，
并且不一样记录之间的“name”值有可能会相同，
如今就是须要查询出在该表中的各记录之间，“name”值存在重复的项；
Select Name,Count(*) From A Group By Name Having Count(*) > 1

若是还查性别也相同大则以下:
Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1


(三)
方法一

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，一是彻底重复的记录，也即全部字段均重复的记录，二是部分关键字段重复的记录，好比Name字段重复，而其余字段不必定重复或都 重复能够忽略。

一、对于第一种重复，比较容易解决，使用

select distinct * from tableName

就能够获得无重复记录的结果集。

若是该表须要删除重复的记录（重复记录保留1条），能够按如下方法删除

select distinct * into #Tmp from tableName

drop table tableName

select * into tableName from #Tmp

drop table #Tmp

发生这种重复的缘由是表设计不周产生的，增长惟一索引列便可解决。

二、这类重复问题一般要求保留重复记录中的第一条记录，操做方法以下

假设有重复的字段为Name,Address，要求获得这两个字段惟一的结果集

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即获得了Name，Address不重复的结果集（但多了一个autoID字段，实际写时能够写在select子句中省去此列）

(四)
查询重复

select * from tablename where id in (

select id from tablename

group by id

having count(id) > 1

)