SQL Sub Query无法正常工作

Question

任何想法为什么这不起作用（基于你在论坛上的例子它应该！）谢谢。

select result.low 
from (
  select top 1 country as low, count() 
  from customers c, orders o 
  where c.customerid=o.customerid 
  group by country 
  order by count()
) as result

Answer 1

如前所述，存在几个问题

select result.low 
from (
  select top 1 country as low, count() -- count() needs an argument and needs to be aliased
  from customers c, orders o           -- old style join
  where c.customerid=o.customerid      
  group by country                     -- column `country` may need qualifying
  order by count()                     -- count() needs an argument
) as result

所以查询应该是

select top 1 country as low
from customers c
join orders o 
on c.customerid=o.customerid 
group by c.country
order by count(*)