SQL 从多列查询 return 最大值

Question

我在 SQL Server 2008 R2 数据库中有以下表格：

Customers
=========
CustID  CustName
======  ========
0       NULL
1       A
2       B
3       C

InterestingCustomers
====================
CustID
======
0
1
3

Orders
======
CustID  OrderID  InvoiceTotal  Discount
======  =======  ============  ========
0       NULL     2000          NULL
0       100      NULL          500      
1       1        100           NULL
1       2        90            15
2       3        300           25
2       4        50            0
3       5        100           10
3       6        200           25
3       7        150           NULL
3       8        120           20

我想要一个查询，显示所有订单中每个 CustID 和 CustName 的 InvoiceTotal 和 Discount 列的最大值，但前提是客户出现在 InterestingCutomers 中并且 ID > 0:

CustID  CustName  MaxInvoiceTotal  MaxDiscount
1       A         100              15
3       C         200              25

我的一个限制是我的应用程序是使用 Jet 4.0 和 ADO 的旧版 VB6。这不支持托管我的数据库的 SQL Server 2008 的许多高级功能。我可用的 SQL 函数列在此处：https://support.microsoft.com/en-us/kb/294698。

到目前为止，我已经能够获得最大的 InvoiceTotal，但我无法扩展相同的查询以达到 return 任何其他列的最大值。

以下正确 return 每个有效 CustID 的最大 InvoiceTotal：

SELECT Customers.CustID, CustName, InvoiceTotal, Discount 
FROM ((Customers INNER JOIN Interesting ON Customers.CustID = Interesting.CustID) INNER JOIN Orders ON Customers.CustID = Orders.CustID) 
WHERE ((CustID > 0) 
AND (InvoiceTotal IN 
(SELECT MAX(InvoiceTotal) AS MaxInvoiceTotal 
FROM Orders 
WHERE Orders.CustID = Customers.CustID)))

Returns:

CustID  CustName  MaxInvoiceTotal
1       A         100            
3       C         200

但是，扩展 WHERE 子句以将 Discount 限制为每个客户的最大值仅 returns 记录，其中 InvoiceTotal 和 Discount 恰好是最大值并且属于同一订单：

WHERE ((CustID > 0) AND (InvoiceTotal IN 
(SELECT MAX(InvoiceTotal) AS MaxInvoiceTotal 
FROM Orders 
WHERE Orders.CustID = Customers.CustID)) AND 
Discount IN 
(SELECT MAX(Discount) AS MaxDiscount 
FROM Orders 
WHERE Orders.CustID = Customers.CustID))

Returns:

CustID  CustName  MaxInvoiceTotal  MaxDiscount
3       C         200              25

未选择 CustID 1，因为它的最大 InvoiceTotal 值与其最大折扣值属于不同的订单。我假设这两个条件都针对每个符合条件的订单进行了测试，但我想要一些方法来删除 OrderID 与 InvoiceTotal 和 Discount 之间的关联。 OR-ing 附加子句不起作用。

我怀疑我可能在 UNION 范围内，但想看看是否有更清洁或更有效的方法，考虑到我列出的限制。

Answer 1

SELECT Customers.CustID, CustName, MaxInvoiceTotal, MaxDiscount 
FROM Customers 
INNER JOIN Interesting ON Customers.CustID = Interesting.CustID
INNER JOIN (SELECT CustID, MAX(Discount) AS MaxDiscount 
            FROM Orders
            Group by CustID) MaxDiscountOrders ON Customers.CustID =     
            MaxDiscountOrders.CustID
INNER JOIN (SELECT CustID, MAX(InvoiceTotal) AS MaxInvoiceTotal 
            FROM Orders
            Group by CustID) MaxInvoiceTotalOrders ON Customers.CustID     
            = MaxInvoiceTotalOrders.CustID
WHERE CustID > 0

试试这个。不过我还没有检查语法错误。

Answer 2

SELECT CustID,
       CustName = MAX(CustName),
       InvoiceTotal = SUM(InvoiceTotal),
       Discount = SUM(Discount)
FROM Orders O
INNER JOIN Customers C ON O.CustID = C.CustID
WHERE O.CustID IN (SELECT CustID 
                   FROM InterestingCustomers)
AND O.CustID>0
GROUP BY CustID

SQL 从多列查询 return 最大值

SQL query to return maximum values from multiple columns

sql-server

vb6