MySQL中查詢、刪除重復記錄的方法大全。本站提示廣大學習愛好者:(MySQL中查詢、刪除重復記錄的方法大全)文章只能為提供參考,不一定能成為您想要的結果。以下是MySQL中查詢、刪除重復記錄的方法大全正文
作者:無喱頭的菜園子
mysql中刪除重復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、刪除重復記錄的方法大全,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於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、對於第一種重復,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
發生這種重復的原因是表設計不周產生的,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
假設有重復的字段為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內容了,希望本文的內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,謝謝大家對的支持。