怎么在tablename是一个参数的表中取字段值？

declare @cc char(11)
declare @output char(30)
declare @tabname sysname
declare @sql sysname
declare @ss varchar(10)
select @tabname='xtblb'
set @sql=N'select @ss=blm from '+ @tabname+' where blz=''2'''
execute sp_executesql
          @sql,
          N'@ss varchar(10) output',
  @ss=@ss output
select @ss