请问如何在表名后加变量？

[tired_bird]

请问如何在表名后加变量？

例如
declare @i int
declare @v_n varchar(100) ,@fname varchar(100)
set @i = 1
while @i<= 10
begin
@fname = 'column1' + cast(@i as varchar)
update a
a.@fname = b.total
from dm a ， dn b
where a.yyear=b.yyear and a.mmonth=1
end

但a.@fname这样出错，请问怎么办，谢谢!

[wzy_love_sly]

看老龟给你答案吧　哈哈

[wzy_love_sly]

要用动态语句，等老龟发，我也留一份

[dawugui]

--要使用动态SQL.
declare @i int 
declare @v_n varchar(100) 
declare @fname varchar(100) 
declare @sql as varchar(100) 
set @i = 1 
while @i <= 10 
begin 
  @fname = 'column1' + cast(@i as varchar) 
  set @sql = 'update a set ' + @fname + ' = b.total from dm a  dn b where a.yyear=b.yyear and a.mmonth=1'
  exec(@sql) 
  set @i = @i + 1
end 

[dawugui]

动态sql语句基本语法 
1 :普通SQL语句可以用Exec执行 

eg:   Select * from tableName 
         Exec('select * from tableName') 
         Exec sp_executesql N'select * from tableName'    -- 请注意字符串前一定要加N 

2:字段名，表名，数据库名之类作为变量时，必须用动态SQL 

eg:   
declare @fname varchar(20) 
set @fname = 'FiledName' 
Select @fname from tableName              -- 错误,不会提示错误，但结果为固定值FiledName,并非所要。 
Exec('select ' + @fname + ' from tableName')     -- 请注意 加号前后的 单引号的边上加空格 

当然将字符串改成变量的形式也可 
declare @fname varchar(20) 
set @fname = 'FiledName' --设置字段名 

declare @s varchar(1000) 
set @s = 'select ' + @fname + ' from tableName' 
Exec(@s)                -- 成功 
exec sp_executesql @s   -- 此句会报错 



declare @s Nvarchar(1000)  -- 注意此处改为nvarchar(1000) 
set @s = 'select ' + @fname + ' from tableName' 
Exec(@s)                -- 成功     
exec sp_executesql @s   -- 此句正确 

3. 输出参数 
declare @num int, 
        @sqls nvarchar(4000) 
set @sqls='select count(*) from tableName' 
exec(@sqls) 
--如何将exec执行结果放入变量中？ 

declare @num int, 
               @sqls nvarchar(4000) 
set @sqls='select @a=count(*) from tableName ' 
exec sp_executesql @sqls,N'@a int output',@num output 
select @num 

[jinjazz]

declare   @i   int   
declare   @v_n   varchar(100)   ,@fname   varchar(100)   
set   @i   =   1   
while   @i <=   10 
begin 
set @fname   =     'column1'   +   cast(@i   as   varchar) 
exec ('update       a       
a.'+@fname+'       =       b.total   
from       dm       a     ，   dn       b   
where       a.yyear=b.yyear       and       a.mmonth=1 ')
set @i=@i+1
end   

[-狙击手-]

declare @i int
declare @v_n varchar(100) ,@fname varchar(100)
set @i = 1
while @i <= 10
begin
set @fname = 'column1' + cast(@i as varchar)
exec('update a '+
a.@fname +' = b.total
from dm a , dn b
where a.yyear=b.yyear and a.mmonth=1 ')
end

[-狙击手-]

declare   @i   int   
declare   @v_n   varchar(100)   ,@fname   varchar(100)   
set   @i   =   1   
while   @i <=   10 
begin 
set @fname = 'column1' + cast(@i   as   varchar) 
exec ('update a       
set a.'+@fname+' = b.total   
from dm a  , dn b   
where a.yyear=b.yyear and a.mmonth=1 ')
set @i=@i+1
end  

[-狙击手-]

上面的回答都少了一个update后的 set

[areswang]

标记下来看看！

[tired_bird]

各位大侠帮帮忙
这几天我用潇洒老乌龟的
declare @i int
declare @v_n varchar(100)
declare @fname varchar(100)
declare @sql as varchar(100)
set @i = 1
while @i <= 10
begin
@fname = 'column1' + cast(@i as varchar)
set @sql = 'update a set ' + @fname + ' = b.total from dm a , dn b where a.yyear=b.yyear and a.mmonth=1'
exec(@sql)
set @i = @i + 1
end

和无枪狙击手的declare @i int
declare @v_n varchar(100) ,@fname varchar(100)
set @i = 1
while @i <= 10
begin
set @fname = 'column1' + cast(@i as varchar)
exec ('update a
set a.'+@fname+' = b.total
from dm a , dn b
where a.yyear=b.yyear and a.mmonth=1 ')
set @i=@i+1
end

方法都提示错误
难道是exec不能和update一起用吗？
请大家号号脉
等待中

[cxmcxm]

只能用动态执行

declare   @i   int   
declare   @v_n   varchar(100)   ,@fname   varchar(100)   
declare @str1 varchar(500)
set   @i   =   1   
while   @i <=   10 
begin 
@fname   =     'column1'   +   cast(@i   as   varchar) 
set @str1='update       a   set '+@fname
+' =  b.total   
from       dm       a     ，   dn       b   
where       a.yyear=b.yyear       and       a.mmonth=1 '
exec (@str1)
end   

[tired_bird]

谢谢，己调通!

[tired_bird]

谢谢，问题按大家的办法得到解决了