前言
本文主要給大家介紹了關(guān)于MySQL中查詢、刪除重復記錄的方法，分享出來供大家參考學習，下面來看看詳細的介紹：
查找所有重復標題的記錄：
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、查找重復記錄
1、查找全部重復記錄
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、刪除重復記錄
1、刪除全部重復記錄（慎用）
Delete 表 Where 重復字段 In (Select 重復字段 From 表 Group By 重復字段 Having Count(*)>1)
2、保留一條（這個應該是大多數(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記錄，重復記錄是根據(jù)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)
2、刪除表中多余的重復記錄，重復記錄是根據(jù)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)
3、查找表中多余的重復記錄（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)
4、刪除表中多余的重復記錄（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)
5、查找表中多余的重復記錄（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)
四、補充
有兩個以上的重復記錄，一是完全重復的記錄，也即所有字段均重復的記錄，二是部分關(guān)鍵字段重復的記錄，比如Name字段重復，而其他字段不一定重復或都重復可以忽略。
1、對于第一種重復，比較容易解決，使用
select distinct * from tableName
就可以得到無重復記錄的結(jié)果集。
如果該表需要刪除重復的記錄（重復記錄保留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)生這種重復的原因是表設(shè)計不周產(chǎn)生的，增加唯一索引列即可解決。
2、這類重復問題通常要求保留重復記錄中的第一條記錄，操作方法如下
假設(shè)有重復的字段為Name,Address，要求得到這兩個字段唯一的結(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)
總結(jié)
以上就是這篇文章的全部內(nèi)容了，希望本文的內(nèi)容對大家的學習或者工作能帶來一定的幫助，如果有疑問大家可以留言交流，謝謝大家對腳本之家的支持。
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