删除表中重複記錄 隻留一條即可

今天碰到一個在上萬條記錄裡,存在着些相同的記錄,隻是主鍵和某個列不同，如何能用SQL語句,删除掉重複的呢?問題解答了很高興，總結下。

1、如果記錄所有字段的值都一樣的，就是完全重複的話，我也覺得用SELECT   DISTINCT   *   FROM   生成一個臨時表，删掉舊表的做法比較好。   

但表的記錄并非完全重複，比如有個主id是唯一的，要求也是把另一個字段name相同的去掉，隻保留一個。   

    delete     from   table   as   a   where   a.id     not   in(select   top   1   id   from   table   as   b   where   a.name   =b.name)  

2、

　　有兩個意義上的重複記錄，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。

　　a、對于第一種重複，比較容易解決，使用

1）、a）、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)

b)、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)

c)、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)

d)、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)

e)、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)

比方說在A表中存在一個字段“name”，而且不同記錄之間的“name”值有可能會相同，

現在就是需要查詢出在該表中的各記錄之間，“name”值存在重複的項；

Select Name,Count(*) From A Group By Name Having Count(*) > 1

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。

　　b、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)

3、執行個體：

A表結構：

ID RQ SJ C

--------------------------------------------

1 2010-07-14 14:20:50 A1

2 2010-02-15 05:12:23 A1

3 2010-07-14 14:20:50 A1

4 2010-06-16 16:16:16 A2

5 2010-06-16 16:16:16 A2

6 2010-05-18 05:10:35 A3

7 2010-02-15 05:12:23 A1

--------------------------------------------

求SQL語句一條，把表A中　RQ,SJ,C　三個字段有相同的重複記錄删除．

得到的結果：

ID RQ SJ C

--------------------------------------------

1 2010-07-14 14:20:50 A1

2 2010-02-15 05:12:23 A1

4 2010-06-16 16:16:16 A2

6 2010-05-18 05:10:35 A3

--------------------------------------------

Delete from A Where ID Not In (Select Min(ID) from A Group By RQ,SJ,C )

Delete a from tb a inner join tb as b on a.fid <b.fid and a.c=b.c and a.rq=b.rq and a.sj=b.sj

delete from A t

where exists(select 1 from A where ID <A.ID and SJ=t.SJ and RQ=t.RQ and C=t.c)