MySQL查詢及刪除重複記錄的方法

MySQL查詢及刪除重複記錄的方法

2009-07-31 17:03

查詢及刪除重複記錄的方法

(一)
一、查找表中多餘的重複記錄，重複記錄是根據單個字段（peopleId）來判斷
select * from people
where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)

二、刪除表中多餘的重複記錄，重複記錄是根據單個字段（peopleId）來判斷，只留有rowid最小的記錄
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、查找表中多餘的重複記錄（多個字段）
select * from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)

四、刪除表中多餘的重複記錄（多個字段），只留有rowid最小的記錄
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) 執行報錯

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

刪除腳本：

#!/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、查找表中多餘的重複記錄（多個字段），不包含rowid最小的記錄
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)
比方說
在A表中存在一個字段「name」，
並且不一樣記錄之間的「name」值有可能會相同，
如今就是須要查詢出在該表中的各記錄之間，「name」值存在重複的項；
Select Name,Count(*) From A Group By Name Having Count(*) > 1

若是還查性別也相同大則以下:
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

有兩個意義上的重複記錄，一是徹底重複的記錄，也即全部字段均重複的記錄，二是部分關鍵字段重複的記錄，好比Name字段重複，而其餘字段不必定重複或都 重複能夠忽略。

一、對於第一種重複，比較容易解決，使用

select distinct * from tableName

就能夠獲得無重複記錄的結果集。

若是該表須要刪除重複的記錄（重複記錄保留1條），能夠按如下方法刪除

select distinct * into #Tmp from tableName

drop table tableName

select * into tableName from #Tmp

drop table #Tmp

發生這種重複的緣由是表設計不周產生的，增長惟一索引列便可解決。

二、這類重複問題一般要求保留重複記錄中的第一條記錄，操做方法以下

假設有重複的字段爲Name,Address，要求獲得這兩個字段惟一的結果集

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)

最後一個select即獲得了Name，Address不重複的結果集（但多了一個autoID字段，實際寫時能夠寫在select子句中省去此列）

(四)
查詢重複

select * from tablename where id in (

select id from tablename

group by id

having count(id) > 1

)