Question

我现在正在使用带有示例数据库的mssql＆＃34; adventureworks 2014＆＃34;，这里我遇到了一些关于join和sum的问题，这里是我使用的两个表：

    CREATE TABLE PurchaseOrderHeader(
   PurchaseOrderID INTEGER  NOT NULL PRIMARY KEY 
  ,VendorID        INTEGER  NOT NULL
  ,OrderDate       VARCHAR(23) NOT NULL
  ,TotalDue        NUMERIC(10,4) NOT NULL
);
INSERT INTO PurchaseOrderHeader(PurchaseOrderID,VendorID,OrderDate,TotalDue) VALUES (1,1580,'2011-04-16 00:00:00.000',222.1492);
INSERT INTO PurchaseOrderHeader(PurchaseOrderID,VendorID,OrderDate,TotalDue) VALUES (2,1496,'2011-04-16 00:00:00.000',300.6721);
INSERT INTO PurchaseOrderHeader(PurchaseOrderID,VendorID,OrderDate,TotalDue) VALUES (3,1494,'2011-04-16 00:00:00.000',9776.2665);
INSERT INTO PurchaseOrderHeader(PurchaseOrderID,VendorID,OrderDate,TotalDue) VALUES (4,1650,'2011-04-16 00:00:00.000',189.0395);
INSERT INTO PurchaseOrderHeader(PurchaseOrderID,VendorID,OrderDate,TotalDue) VALUES (5,1654,'2011-04-30 00:00:00.000',22539.0165);
INSERT INTO PurchaseOrderHeader(PurchaseOrderID,VendorID,OrderDate,TotalDue) VALUES (6,1664,'2011-04-30 00:00:00.000',16164.0229);
INSERT INTO PurchaseOrderHeader(PurchaseOrderID,VendorID,OrderDate,TotalDue) VALUES (7,1678,'2011-04-30 00:00:00.000',64847.5328);


       CREATE TABLE PurchaseOrderDetail(
   PurchaseOrderID       INTEGER  NOT NULL
  ,PurchaseOrderDetailID INTEGER  NOT NULL PRIMARY KEY 
  ,OrderQty              INTEGER  NOT NULL
  ,ProductID             INTEGER  NOT NULL
);
INSERT INTO PurchaseOrderDetail(PurchaseOrderID,PurchaseOrderDetailID,OrderQty,ProductID) VALUES (1,1,4,1);
INSERT INTO PurchaseOrderDetail(PurchaseOrderID,PurchaseOrderDetailID,OrderQty,ProductID) VALUES (2,2,3,359);
INSERT INTO PurchaseOrderDetail(PurchaseOrderID,PurchaseOrderDetailID,OrderQty,ProductID) VALUES (2,3,3,360);
INSERT INTO PurchaseOrderDetail(PurchaseOrderID,PurchaseOrderDetailID,OrderQty,ProductID) VALUES (3,4,550,530);
INSERT INTO PurchaseOrderDetail(PurchaseOrderID,PurchaseOrderDetailID,OrderQty,ProductID) VALUES (4,5,3,4);
INSERT INTO PurchaseOrderDetail(PurchaseOrderID,PurchaseOrderDetailID,OrderQty,ProductID) VALUES (5,6,550,512);
INSERT INTO PurchaseOrderDetail(PurchaseOrderID,PurchaseOrderDetailID,OrderQty,ProductID) VALUES (6,7,550,513);
INSERT INTO PurchaseOrderDetail(PurchaseOrderID,PurchaseOrderDetailID,OrderQty,ProductID) VALUES (7,8,550,317);
INSERT INTO PurchaseOrderDetail(PurchaseOrderID,PurchaseOrderDetailID,OrderQty,ProductID) VALUES (7,9,550,318);
INSERT INTO PurchaseOrderDetail(PurchaseOrderID,PurchaseOrderDetailID,OrderQty,ProductID) VALUES (7,10,550,319);

这是sql脚本：

select PurchaseOrderHeader.VendorID,
SUM(CASE WHEN Datename(year,PurchaseOrderHeader.OrderDate) = 2011 THEN PurchaseOrderHeader.TotalDue else 0 END) as "TotalPay IN 2011", 
SUM(CASE WHEN Datename(year,PurchaseOrderHeader.OrderDate) = 2011 THEN PurchaseOrderDetail.OrderQty else 0 END) as "TotalOrder IN 2011"
from PurchaseOrderHeader
left join PurchaseOrderDetail on PurchaseOrderHeader.PurchaseOrderID = PurchaseOrderDetail.PurchaseOrderID
group by PurchaseOrderHeader.VendorID
order by VendorID

这是我的代码：

VendorID    TotalPay IN 2011    TotalOrder IN 2011
1494        9776.2665           550
1496        601.3442            6
1580        222.1492            4
1650        189.0395            3
1654        22539.0165          550
1664        16164.0229          550
1678        194542.5984         1650

这是我得到的：

VendorID    TotalPay IN 2011    TotalOrder IN 2011
1494        9776.2665           550
1496        300.6721            6
1580        222.1492            4
1650        189.0395            3
1654        22539.0165          550
1664        16164.0229          550
1678        64847.5328          1650

虽然我应该期待：

{{1}}

此代码将在PurchaseOrderID上连接两个表，并计算按vendorID分组的TotalDue。问题是当我使用join时，表PurchaseOrderDetail中的多行将引用表PurchaseOrderHeader中的一行。在供应商1496和1678的此示例中，有两行或三行引用PurchaseDetailHeader中的一行。所以它会被添加两到三次。我该怎样避免多次添加，谢谢！

Answer 1

你可以把你的SUM除以COUNT。这样的事情。

select PurchaseOrderHeader.VendorID, 
SUM(CASE WHEN Datename(year,PurchaseOrderHeader.OrderDate) = 2011 THEN PurchaseOrderHeader.TotalDue else 0 END) / COUNT(*) as "TotalPay IN 2011", 
SUM(CASE WHEN Datename(year,PurchaseOrderHeader.OrderDate) = 2011 THEN PurchaseOrderDetail.OrderQty else 0 END) / COUNT(*) as "TotalOrder IN 2011"
from Purchasing.PurchaseOrderHeader
left join Purchasing.PurchaseOrderDetail on PurchaseOrderHeader.PurchaseOrderID = PurchaseOrderDetail.PurchaseOrderID
group by PurchaseOrderHeader.VendorID
order by VendorID

Answer 2

select  h.VendorID,
        SUM(CASE WHEN Datename(year,h.OrderDate) = 2011 THEN h.TotalDue else 0 END) as "TotalPay IN 2011", 
        SUM(CASE WHEN Datename(year,h.OrderDate) = 2011 THEN d.OrderQty else 0 END) as "TotalOrder IN 2011"
from    PurchaseOrderHeader h
left    join (
        select  t.PurchaseOrderID,
                sum(t.OrderQty) as OrderQty
        from    PurchaseOrderDetail t
        group   by t.PurchaseOrderID
        ) d on d.PurchaseOrderID = h.PurchaseOrderID
group by h.VendorID
order by VendorID

Answer 3

避免重复计算的默认方法是使用SUM(DISTINCT expr)。

这并不总是运行得很好，因为您不想对不同的值求和，而是希望对不同的行求和，即使这些行共享相同的值。

解决方案是使用子查询对订单号的详细信息求和，然后加入结果。然后，每个订单ID只有一个要加入订单行：

SELECT PurchaseOrderHeader.VendorID, 
  SUM(PurchaseOrderHeader.TotalDue) AS "TotalPay IN 2011", 
  SUM(POD.Qty) AS "TotalOrder IN 2011"
FROM PurchaseOrderHeader 
LEFT JOIN (
    SELECT PurchaseOrderDetail.PurchaseOrderID, SUM(OrderQty) AS Qty
    FROM PurchaseOrderDetail 
    GROUP BY PurchaseOrderDetail.PurchaseOrderID
   ) AS POD on PurchaseOrderHeader.PurchaseOrderID = POD.PurchaseOrderID
WHERE Datename(year,PurchaseOrderHeader.OrderDate) = 2011 
GROUP BY PurchaseOrderHeader.VendorID
ORDER BY VendorID

此外，我还可以自由地从查询的CASE WHEN到SUM()部分删除WHERE语句。在这种情况下，应该使用较短的代码给出相同的结果。

Answer 4

很多好的答案，但我认为他们错过了供应商可能有多个采购订单的位置，并且抛出了TotalOrder的计算方式。（尝试一个包含多个订单的多个供应商的示例，每个订单都有多个详细信息。）不要忘记检查可能的NULL值！

在这里，我使用子查询来计算相关年份的每个供应商的TotalPay，然后将其加入到所有供应商的列表中。（为了易读性，也提入表别名。）

--  As a subquery
SELECT
   hd.VendorID,
  ,sum(case
         when year(hd.OrderDate) = 2011 then hd.TotalDue
         else 0
       end)                             as "TotalPay IN 2011"
  ,isnull(subQuery.TotaOrderIn2011, 0)  as "TotalOrder IN 2011"
 from PurchaseOrderHeader hd
  left join (--  Calculate volume by vendor for 2011
             select 
                hd.VendorID
               ,sum(OrderQty)  TotalOrderIn2011
              from PurchaseOrderHeader hd
               inner join PurchaseOrderDetail dt 
                on hd.PurchaseOrderID = dt.PurchaseOrderID
              where year(hd.OrderDate) = 2011
              group by
                hd.VendorID
    ) subQuery
   on subQuery.VendorId = hd.VendorId
 group by hd.VendorID
 order by hd.VendorID

如何在使用连接时避免多次求和

4 个答案: