sql查詢重復記錄、刪除重復記錄方法大全

jopen 10年前發布 | 14K 次閱讀 SQL

查找所有重復標題的記錄：

    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 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)
 
    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)
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