前言

本文主要給大家介紹了關(guān)于MySQL中查詢、刪除重復(fù)記錄的方法，分享出來供大家參考學(xué)習(xí)，下面來看看詳細(xì)的介紹：

查找所有重復(fù)標(biāo)題的記錄：

select title,count(*) as count from user_table group by title having count>1;

SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC

一、查找重復(fù)記錄

1、查找全部重復(fù)記錄

SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC

2、過濾重復(fù)記錄(只顯示一條)

Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)

注：此處顯示ID最大一條記錄

二、刪除重復(fù)記錄

1、刪除全部重復(fù)記錄(慎用)

Delete 表 Where 重復(fù)字段 In (Select 重復(fù)字段 From 表 Group By 重復(fù)字段 Having Count(*)>1)

2、保留一條(這個(gè)應(yīng)該是大多數(shù)人所需要的 _)

Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title)

注：此處保留ID最大一條記錄

三、舉例

1、查找表中多余的重復(fù)記錄，重復(fù)記錄是根據(jù)單個(gè)字段(peopleId)來判斷

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

2、刪除表中多余的重復(fù)記錄，重復(fù)記錄是根據(jù)單個(gè)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)

3、查找表中多余的重復(fù)記錄(多個(gè)字段)

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

4、刪除表中多余的重復(fù)記錄(多個(gè)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)

5、查找表中多余的重復(fù)記錄(多個(gè)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)

四、補(bǔ)充

有兩個(gè)以上的重復(fù)記錄，一是完全重復(fù)的記錄，也即所有字段均重復(fù)的記錄，二是部分關(guān)鍵字段重復(fù)的記錄，比如Name字段重復(fù)，而其他字段不一定重復(fù)或都重復(fù)可以忽略。

1、對于第一種重復(fù)，比較容易解決，使用

select distinct * from tableName

就可以得到無重復(fù)記錄的結(jié)果集。

如果該表需要刪除重復(fù)的記錄(重復(fù)記錄保留1條)，可以按以下方法刪除

select distinct * into #Tmp from tableName

drop table tableName

select * into tableName from #Tmp

drop table #Tmp

發(fā)生這種重復(fù)的原因是表設(shè)計(jì)不周產(chǎn)生的，增加唯一索引列即可解決。

2、這類重復(fù)問題通常要求保留重復(fù)記錄中的第一條記錄，操作方法如下

假設(shè)有重復(fù)的字段為Name,Address，要求得到這兩個(gè)字段唯一的結(jié)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)

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