SQL删除重复记录的方法

MySQL查询及删除重复记录的方法


(一)
1、查找表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断
select * from people
where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)

2、删除表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断，只留有rowid最小的记录
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、查找表中多余的重复记录（多个字段）
select * from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)

4、删除表中多余的重复记录（多个字段），只留有rowid最小的记录
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、查找表中多余的重复记录（多个字段），不包含rowid最小的记录
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)

(二)
比方说
在A表中存在一个字段“name”，
而且不同记录之间的“name”值有可能会相同，
现在就是需要查询出在该表中的各记录之间，“name”值存在重复的项；
Select Name,Count(*) From A Group By Name Having Count(*) > 1

如果还查性别也相同大则如下:
Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1


(三)
方法一

declare @max integer,@id integer

declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >； 1

open cur_rows

fetch cur_rows into @id,@max

while @@fetch_status=0

begin

select @max = @max -1

set rowcount @max

delete from 表名 where 主字段 = @id

fetch cur_rows into @id,@max

end

close cur_rows

set rowcount 0

方法二

　　有两个意义上的重复记录，一是完全重复的记录，也即所有字段均重复的记录，二是部分关键字段重复的记录，比如Name字段重复，而其他字段不一定重复或都重复可以忽略。

　　1、对于第一种重复，比较容易解决，使用

select distinct * from tableName

　　就可以得到无重复记录的结果集。

　　如果该表需要删除重复的记录（重复记录保留1条），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

　　发生这种重复的原因是表设计不周产生的，增加唯一索引列即可解决。

　　2、这类重复问题通常要求保留重复记录中的第一条记录，操作方法如下

　　假设有重复的字段为Name,Address，要求得到这两个字段唯一的结果集

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)

　　最后一个select即得到了Name，Address不重复的结果集（但多了一个autoID字段，实际写时可以写在select子句中省去此列）

(四)
查询重复

select * from tablename where id in (

select id from tablename

group by id

having count(id) > 1

)


本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/softwave/archive/2009/02/14/3890576.aspx

 

delete t1 from 表名 t1,(select a,b,c,d,max(id)as max_id from 表名 groupby a,b,c,d) t2where t1.a=t2.aand t1.b=t2.band t1.c=t2.cand t1.d=t2.dand a.id<>b.max_id

delete   表   where   [id]   not   in   (select   max([id])   from   表   group   by   a,b   )
--a,b为你要规定的列

借用dawugui(潇洒老乌龟)的表
CREATE   TABLE   Tb1(id   int,   [a]   varchar(255),   [b]   varchar(255),   [c]   varchar(255),   [d]   varchar(255))
INSERT   Tb1(id,   [a],   [b],   [c],   [d])
                      SELECT   1,   '1 ', '2 ', '3 ', '4 '
UNION   ALL     SELECT   2,   '1 ', '5 ', '3 ', '5 '
UNION   ALL     SELECT   3,   '1 ', '2 ', '7 ', '9 '
UNION   ALL     SELECT   4,   '1 ', '4 ', '7 ', '6 '

delete   from     Tb1   where   [id]   not   in  
(select   min([id])   from   Tb1   a   where   a=Tb1.a   and   b=Tb1.b)
这样也行
delete   from     Tb1   where   [id]   not   in  
(select   top   1   [id]     from   Tb1   a   where   a=Tb1.a   and   b=Tb1.b)

 

PostgreSQL 删除多字段重复的记录

关键字: 数据库 目标删除数据量不是很大的情况下，数据库表多字段的重复的记录:
id为sequence

 

1. create table table_tmp   
2. as (select distinct aa,bb,cc,dd from table);-----创建临时表，并保存不重复的数据  
3.   
4. truncate stompcomment cascade----清空原表数据，并清空通过外键约束引用被清空的表的表  
5. 或者，delete from stompcomment;-----清空原表数据  
6. 两者不同是前者可以立即回收表的存储空间  
7.   
8. insert into table select nextval('table_sequence'::regclass) as seq,* from table_tmp----将临时表的数据写回到原表中  
9.   
10. drop table table_tmp;--------删除临时表 
    

 

MYSQL 删除重复数据（单个字段）：

查询：

select t1.user_code from sys_users t1,(select user_code,min(user_id) as minid from sys_users 
group by user_code having count(user_code)>1) t2 where t1.user_code=t2.user_code and t1.user_id<>t2.minid; 



删除：
delete user1 from sys_users user1,(select t1.user_id from sys_users t1,
(select user_code,min(user_id) as minid from sys_users group by user_code having count(user_code)>1) t2 
where t1.user_code=t2.user_code and t1.user_id<>t2.minid) user2 where user1.user_id=user2.user_id