用SQL语句删除重复记录的四种方法

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

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

 

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。

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