如何在 SQL GROUP BY 子句中返回空组

Question

我有一个查询来返回每个位置的合同内和合同外花费了多少，返回如下内容：

Location     | ContractStatus | Expenses
-------------+----------------+---------
New York     | Ad-hoc         | 2043.47
New York     | Contracted     | 2894.57
Philadelphia | Ad-hoc         | 3922.53
Seattle      | Contracted     | 2522.00

问题是，对于所有临时或所有合同费用的位置，我只能得到一行。我想为每个位置取回两行，如下所示：

Location     | ContractStatus | Expenses
-------------+----------------+---------
New York     | Ad-hoc         | 2043.47
New York     | Contracted     | 2894.57
Philadelphia | Ad-hoc         | 3922.53
Philadelphia | Contracted     |    0.00
Seattle      | Ad-hoc         |    0.00
Seattle      | Contracted     | 2522.00

有什么办法可以通过 SQL 完成此操作吗？这是我正在使用的实际查询（SQL Server 2005）：

SELECT Location, 
     CASE WHEN Orders.Contract_ID IS NULL 
          THEN 'Ad-hoc' ELSE 'Contracted' END 
                     AS ContractStatus,
     SUM(OrderTotal) AS Expenses
FROM Orders
GROUP BY Location, 
    CASE WHEN Orders.Contract_ID IS NULL 
         THEN 'Ad-hoc' ELSE 'Contracted' END
ORDER BY Location ASC, ContractStatus ASC

Answer 1

是的，构造一个表达式，仅返回 adhoc 的 ordertotal，为其他返回 0，以及另一个执行相反操作的表达式，并对这些表达式求和。这将包括每个位置一行和两列，一列用于临时，一列用于合同...

 SELECT Location,  
     Sum(Case When Contract_ID Is Null Then OrderTotal Else 0 End) AdHoc,
     Sum(Case When Contract_ID Is Null Then 0 Else OrderTotal  End) Contracted
 FROM Orders 
 GROUP BY Location

如果您确实想要为每个单独的行，那么一种方法是：

 SELECT Location, Min('AdHoc') ContractStatus,
     Sum(Case When Contract_ID Is Null 
              Then OrderTotal Else 0 End) OrderTotal
 FROM Orders 
 GROUP BY Location
 Union
 SELECT Location, Min('Contracted') ContractStatus,
     Sum(Case When Contract_ID Is Null 
              Then 0 Else OrderTotal  End) OrderTotal
 FROM Orders 
 GROUP BY Location
 Order By Location