如何在 SQL GROUP BY 子句中返回空组

Question

我有一个查询返回在每个位置的合同和合同外花费了多少，它返回如下内容：

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地点，我只能得到一行。我想为每个位置返回两行，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

有什么方法可以通过 SQL 来完成吗？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，它只为 adhoc 返回 ordertotal，为其他返回 0，另一个相反的表达式，并对这些表达式求和。这将包括每个位置一行，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

如果你真的想为每个单独的行，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

Answer 2

您需要先填充不同位置和合同的列表。看到这个查询，它可能有一些语法错误，因为我没有运行它。

;WITH Locations AS 
(
    SELECT DISTINCT Location, 1 as ContractStatus
    FROM    Orders 
    UNION 
    SELECT DISTINCT Location, 2 as ContractStatus
    FROM    Orders
)

SELECT  Location, 
        CASE 
            WHEN L.ContractStatus = 1 THEN 'Ad-hoc'
            ELSE 'Contracted'
        END, 
        ISNULL(SUM(OrderTotal),0) Expenses
FROM    Locations L
    LEFT JOIN Orders O 
        ON L.Location = O.Location AND L.ContractStatus = CASE WHEN O.Contract_ID IS NULL THEN 1 ELSE 2 END
GROUP BY    L.Location, 
            CASE 
                WHEN L.ContractStatus = 1 THEN 'Ad-hoc'
                ELSE 'Contracted'
            END 

Answer 3

在分组之前，您必须以某种方式为每个位置创建至少一行的每个状态。这是一种方法：

SELECT s.Location, s.ContractStatus, ISNULL(o.Expenses, 0) AS Expenses
FROM
(
    SELECT
        Location,
        CASE
            WHEN Contract_ID IS NULL THEN 'Ad-hoc'
            ELSE 'Contracted'
        END AS ContractStatus,
        SUM(OrderTotal) AS Expenses
    FROM Orders
    GROUP BY
        Location,
        CASE WHEN Contract_ID IS NULL THEN 'Ad-hoc' ELSE 'Contracted' END)
) o
RIGHT JOIN
(
    SELECT DISTINCT o.Location, s1.ContractStatus
    FROM Orders o
    CROSS JOIN
    (
        SELECT 'Ad-hoc' AS ContractStatus
        UNION ALL
        SELECT 'Contracted'
    ) s1
) s
ON s.Location = o.Location
AND s.ContractStatus = o.ContractStatus

编辑：我不确定 DISTINCT/CROSS JOIN 组合的性能，但如果它是一次性或不经常使用的查询，应该没问题。

Answer 4

以前的大多数解决方案都依赖于确切知道第二列有多少，虽然我不是 SQL 专家，但我有一个用例，其中每个 @ 的 ContractStatus 的数量是未知的987654324@.

所以我找到了How to merge 2 columns with all possible combinations in SQL?，它展示了如何处理任意数量的不同次要指标。

http://sqlfiddle.com/#!18/72236b/3/0

CREATE TABLE Table1
    ([Location] varchar(12), [ContractStatus] varchar(10), [Expenses] int)
;
    
INSERT INTO Table1
    ([Location], [ContractStatus], [Expenses])
VALUES
    ('New York', 'Ad-hoc', 2043.47),
    ('New York', 'Contracted', 2894.57),
    ('Philadelphia', 'Ad-hoc', 3922.53),
    ('Seattle', 'Contracted', 2522.00)
;

-- Use CTE to get all possibilities
with possibilities as (
    select l.Location, c.ContractStatus
    from (select distinct Location from [Table1]) l cross join
         (select distinct ContractStatus from [Table1]) c
)
select
    p.Location
    ,p.ContractStatus
    -- Choose the proper agg function here
    ,sum([Expenses]) as Expenses
from possibilities p 
left join [Table1] t on p.Location = t.Location and p.ContractStatus = t.ContractStatus
group by p.Location, p.ContractStatus
order by Location, ContractStatus