SQL中查询没有记录如何返回0?

字段名：field1

表名：table1

语法：select  top 1 isnull(field1,0) as 'field2' from table1 c1 join table2 c2 on c1.id1=c2.id2 where 条件...

例子：

select top 1 isnull(max(s.ID) ,0) as id
      from Size s join ClassSize cs on cs.SizeID=s.ID where cus_id=1 AND SizeName='大号' AND cs.ClassID=1