《Mysql必讀MySQL中查詢、刪除重復記錄的方法大全》要點：
本文介紹了Mysql必讀MySQL中查詢、刪除重復記錄的方法大全，希望對您有用。如果有疑問，可以聯系我們。
MYSQL應用前言
MYSQL應用本文主要給大家介紹了關于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：
MYSQL應用查找所有重復標題的記錄：
MYSQL應用
select title,count(*) as count from user_table group by title having count>1;
MYSQL應用
SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
MYSQL應用一、查找重復記錄
MYSQL應用1、查找全部重復記錄
MYSQL應用
SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
MYSQL應用2、過濾重復記錄(只顯示一條)
MYSQL應用
Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)
MYSQL應用注：此處顯示ID最大一條記錄
MYSQL應用二、刪除重復記錄
MYSQL應用1、刪除全部重復記錄(慎用)
MYSQL應用
Delete 表 Where 重復字段 In (Select 重復字段 From 表 Group By 重復字段 Having Count(*)>1)
MYSQL應用2、保留一條(這個應該是大多數人所需要的 ^_^)
MYSQL應用
Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title)
MYSQL應用注：此處保留ID最大一條記錄
MYSQL應用三、舉例
MYSQL應用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
MYSQL應用
select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
MYSQL應用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
MYSQL應用
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)
MYSQL應用3、查找表中多余的重復記錄(多個字段)
MYSQL應用
select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
MYSQL應用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
MYSQL應用
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)
MYSQL應用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
MYSQL應用
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)
MYSQL應用四、補充
MYSQL應用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.
MYSQL應用1、對于第一種重復,比較容易解決,使用
MYSQL應用
select distinct * from tableName
MYSQL應用就可以得到無重復記錄的結果集.
MYSQL應用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
MYSQL應用
select distinct * into #Tmp from tableName
drop table tableName
select * into tableName from #Tmp
drop table #Tmp
MYSQL應用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.
MYSQL應用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
MYSQL應用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
MYSQL應用
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)
MYSQL應用總結
MYSQL應用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,謝謝大家對維易PHP的支持.
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