MySQL中查詢、删除重複記錄的方法大全

mysql中删除重複記錄的方法有很多種，下面這篇文章主要給大家總結了在MySQL中查詢、删除重複記錄的方法大全，文中給出了詳細的示例代碼供大家參考學習，需要的朋友下面來一起看看吧。

前言

本文主要給大家介紹了關于MySQL中查詢、删除重複記錄的方法，分享出來供大家參考學習，下面來看看詳細的介紹：

查找所有重複标題的記錄：

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、查找重複記錄

1、查找全部重複記錄

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

2、過濾重複記錄(隻顯示一條)

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、删除重複記錄

1、删除全部重複記錄（慎用）

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

2、保留一條（這個應該是大多數人所需要的 ^_^）

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)

2、删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，隻留有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)

4、删除表中多餘的重複記錄（多個字段），隻留有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)

四、補充

有兩個以上的重複記錄，一是完全重複的記錄，也即所有字段均重複的記錄，二是部分關鍵字段重複的記錄，比如Name字段重複，而其他字段不一定重複或都重複可以忽略。

1、對于第一種重複，比較容易解決，使用

select distinct * from tableName

就可以得到無重複記錄的結果集。

如果該表需要删除重複的記錄（重複記錄保留1條），可以按以下方法删除

select distinct * into #Tmp from tableName

drop table tableName

select * into tableName from #Tmp

drop table #Tmp

發生這種重複的原因是表設計不周産生的，增加唯一索引列即可解決。

2、這類重複問題通常要求保留重複記錄中的第一條記錄，操作方法如下

假設有重複的字段為Name,Address，要求得到這兩個字段唯一的結果集

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)

總結

以上就是這篇文章的全部内容了，希望本文的内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援。