用表名作为参数,如何获取查询结果.
declare   @autoid   int
declare   @nautoid   int
declare   @sql   nvarchar(2000)
declare   @tablename   nvarchar(200)
declare   @field   nvarchar(50)
set   @tablename= 'tbl_calendarday '
set   @field= 'cid '
set   @sql= 'select   @nautoid=max( '   +   @field   +   ')   from   '   +   @tablename   +   ' '
print   @sql
exec(@sql)


执行到
set   @sql= 'select   @nautoid=max( '   +   @field   +   ')   from   '   +   @tablename   +   ' '
这句就出错了,请问应该如何解决呢?
错误信息:Must   declare   the   variable   '@nautoid '.



------解决方案--------------------
declare @autoid int
declare @nautoid int
declare @sql nvarchar(2000)
declare @tablename nvarchar(200)
declare @field nvarchar(50)
set @tablename= 'sysobjects '
set @field= 'id '
set @sql= 'select @autoid=max( ' + @field + ') from ' + @tablename
--print @sql
exec sp_executesql @sql,N '@autoid int output ',@autoid output
print @autoid