四种SQL语句删除重复记录的方法

 

问题：如何把具有相同字段的记录删除，只留下一条。

 

例如：表test里有id，name字段，如果有name相同的记录只留下一条，其余的删除。name的内容不定，相同的记录数不定。

 

用SQL语句删除重复记录的四种方法：

方法1：

 

1、将重复的记录记入temp1表

 

select [标志字段id],count(*) into temp1 from [表名] group by [标志字段id] having count(*)>1 软件开发网 www.mscto.com

2、将不重复的记录记入temp1表

 

insert temp1 select [标志字段id],count(*) from [表名] group by [标志字段id] having count(*)=1

 

3、作一个包含所有不重复记录的表

 

select * into temp2 from [表名] where 标志字段id in(select 标志字段id from temp1)

 

4、删除重复表:delete [表名]

 

5、恢复表

insert [表名] select * from temp2

6、删除临时表

drop table temp1 drop table temp2 软件开发网 www.mscto.com

 

方法2：

declare @max integer,@id integer declare cur_rows cursor local for select id,count(*) from 表名 group by id 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 id = @id fetch cur_rows into @id,@max end close cur_rows set rowcount 0

注：set rowcount @max - 1表示当前缓冲区只容纳@max-1条记录，如果有十条重复的，就刪除10条，一定会留一条的。也可以写成delete from 表名。

 

方法3：

 

create table a_dist(id int,name varchar(20)) 
 
 
    
    
    
    

     
     
     
     insert into a_dist values(1,'abc')
     
     
     
     
insert into a_dist values(1,'abc')
     
     
     
     
insert into a_dist values(1,'abc')
     
     
     
     
insert into a_dist values(1,'abc')
    
    
    
    
    
    
    
    

     
     
     
     exec up_distinct 'a_dist','id'
    
    
    
    
    
    
    
    

     
     
     
     select * from a_dist
    
    
    
    
    
    
    
    

     
     
     
     create procedure up_distinct(@t_name varchar(30)
     
     
     
     
,@f_key varchar(30))
     
     
     
     
--f_key表示是分组字段﹐即主键字段
     
     
     
     
as
     
     
     
     
begin
     
     
     
     
declare @max integer,@id varchar(30) ,
     
     
     
     
@sql varchar(7999) ,@type integer
     
     
     
     
select @sql = 'declare cur_rows cursor 
     
     
     
     
for select '+@f_key+' ,count(*) from ' 
     
     
     
     
+@t_name +' group by ' +@f_key +' having count(*) > 1'
     
     
     
     
exec(@sql)
     
     
     
     
open cur_rows 
     
     
     
     
fetch cur_rows into @id,@max 
     
     
     
     
while @@fetch_status=0 
     
     
     
     
begin 
     
     
     
     
select @max = @max -1 
     
     
     
     
set rowcount @max 
     
     
     
     
select @type = xtype from syscolumns 
     
     
     
     
where id=object_id(@t_name) and name=@f_key
     
     
     
     
if @type=56
     
     
     
     
select @sql = 'delete from '+@t_name+' 
     
     
     
     
where ' + @f_key+' = '+ @id 
     
     
     
     
if @type=167  
     
     
     
     
select @sql = 'delete from '+@t_name+' 
     
     
     
     
where ' + @f_key+' = '+''''+ @id +'''' 
     
     
     
     
exec(@sql)
     
     
     
     
fetch cur_rows into @id,@max 
     
     
     
     
end 
     
     
     
     
close cur_rows 
     
     
     
     
deallocate cur_rows
     
     
     
     
set rowcount 0
     
     
     
     
end
    
    
    
    
    
    
    
    

     
     
     
     select * from systypes
     
     
     
     
select * from syscolumns where 
     
     
     
     
id = object_id('a_dist')
     
     
     
     

     
     
     
     

     
     
     
     

     
     
     
     
 
       方法4： 
     
     
     
     
     

     
     
     
     
 
      
 
      
 
       
 
        
 
         
可以用IGNORE_DUP_KEY：  
 
 
 
           
           
           
           

            
            
            
            
create table dup (id int identity not null,
            
            
            
            
name varchar(50)not null)
            
            
            
            
go
            
            
            
            
insert into dup(name) values ('abc')
            
            
            
            
insert into dup(name) values ('abc')
            
            
            
            
insert into dup(name) values ('abc')
            
            
            
            
insert into dup(name) values ('abc')
            
            
            
            
insert into dup(name) values ('abc')
            
            
            
            
insert into dup(name) values ('abc')
            
            
            
            
insert into dup(name) values ('abc')
            
            
            
            
insert into dup(name) values ('cdefg')
            
            
            
            
insert into dup(name) values ('xyz')
            
            
            
            
insert into dup(name) values ('xyz')
            
            
            
            
go
            
            
            
            
select *
            
            
            
            
from dup
            
            
            
            
go
            
            
            
            
create table tempdb..wk(id int not null, 
            
            
            
            
name varchar(50)not null)
            
            
            
            
go
            
            
            
            
create unique index idx_remove_dup 
            
            
            
            
on tempdb..wk(name)
            
            
            
            
with IGNORE_DUP_KEY 
            
            
            
            
go
            
            
            
            
INSERT INTO tempdb..wk (id, name)
            
            
            
            
select id, name
            
            
            
            
from dup
            
            
            
            
go
            
            
            
            
select *
            
            
            
            
from tempdb..wk
            
            
            
            
go
            
            
            
            
delete from dup
            
            
            
            
go
            
            
            
            
set identity_insert dup on
           
           
           
           
           
           
           
           

            
            
            
            INSERT INTO dup (id, name)
            
            
            
            
select id, name
            
            
            
            
from tempdb..wk 
            
            
            
            
 
 
            
            
            
            
go
            
            
            
            
set identity_insert dup off
            
            
            
            
go
            
            
            
            
select *
            
            
            
            
from dup
           
           
           
           
           
           
           
           

            
            
            
            go
            
            
            
            

           
           
           
           
  
 
 
        
 
       
 
      
   
     

     
     
     
     


     
     
     
     

       注释：此处delete原表，再加入不重复的值。大家也可以通过join只delete原表中重复的值。 
     

    
    
    
    

原文： http://www.mscto.com/SqlServer/031041606.html