sql查詢重復記錄、刪除重復記錄方法大全

　　查找所有重復標題的記錄：

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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

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

　　2、過濾重復記錄(只顯示一條)

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1 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)

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1 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 ^_^)

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1 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

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1 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

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1 2 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)

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1 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

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1 2 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

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1 2 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

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1 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

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1 2 3 4 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

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1 2 3 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)