SQL Practice：多次排序

Question

我和老师给出了一些练习题。

到目前为止：

select Sup.supplierID, SupplierName, sum(OD.Quantity) 
as ItemSupplied from Suppliers as Sup
inner join Products as P on Sup.SupplierID=P.SupplierID 
inner join OrderDetails as OD on
P.ProductID=OD.ProductID
group by Sup.supplierID order by ItemSupplied DESC, SupplierName ASC;

我老师的回答是什么样的（带有SupplierID的回答）：

我的问题是我没有和老师一样的答案。 哪一部分我错了？

我通过将sum（）更改为COUNT（DISTINCT [OrderDetails的ProductID]）得到了它 和ORDER BY此COUNT（DISTINCT [来自OrderDetails的ProductID]）首先在DESC中，然后在ASC中的SupplierName：

select Sup.supplierID, SupplierName, count(DISTINCT OD.ProductID) 
as ItemSupplied from Suppliers as Sup
inner join Products as P on Sup.SupplierID=P.SupplierID 
inner join OrderDetails as OD on
P.ProductID=OD.ProductID
group by Sup.supplierID order by ItemSupplied DESC, SupplierName ASC;

Answer 1

我怀疑您的老师正在寻找所提供产品的“计数”，如目录中的项目数量。不是订购商品的总数量。规范不是很清楚。

 SELECT s.supplierid
      , s.suppliername
      , COUNT(p.productid)  AS cnt_items
   FROM Products p
   JOIN Suppliers s
     ON s.supplierid = p.supplierid  
  GROUP
     BY s.supplierid
      , s.suppliername
  ORDER
     BY COUNT(p.productid) DESC
      , s.suppliername ASC

如果我们想要订购已经订购的商品数量，那么供应商的产品数量至少会出现在一个订单上......

 SELECT s.supplierid
      , s.suppliername
      , COUNT(DISTINCT o.productid) AS cnt_items
   FROM Products p
   JOIN Suppliers s
     ON s.supplierid = p.supplierid  
   JOIN OrderDetails o
     ON o.productid = p.productid
  GROUP
     BY s.supplierid
      , s.suppliername
  ORDER
     BY COUNT(DISTINCT o.productid) DESC
      , s.suppliername ASC

Answer 2

您在组中缺少SupplierName。查询应该失败。