declare @sql varchar(500)
select @sql='select * from '+@dbName+'..tableName'
--此句用于执行拼接好的SQL语句
exec(@sql)

例二：
declare @sql2 varchar(max)
declare @str1 varchar(20)
set @str1='年龄'
select @sql2='select Name as 姓名,Age as '+@str1+ case when 1<2 then ',Sex' else '' end+ ' from CBO_Person'
exec(@sql2)