在 SQL Server 2008 中使用条件聚合

Question

我有一个包含太多 select 语句的查询。因此我使用了条件聚合。查询引用 Instock table 中 SQL Server 2008 中的数据，最终查询如下所示：

select 
    SUM(CASE WHEN MONTH = '2013-8-1' THEN CurrentStock ELSE 0 END) as CurrentStock,
    Isnull(Sum(CASE WHEN MONTH = '2014-2-1' THEN CPU ELSE 0 END), 0) - Isnull(Sum(CASE WHEN MONTH = '2013-8-1' THEN CPU ELSE 0 END), 0) as CPU,
    SUM(CASE WHEN Month = '2013-8-1' THEN NonCPUWIP ELSE 0 END) as NonCPU,
    Isnull(Sum(CASE WHEN MONTH = '2014-2-1' THEN ScrapDiscarded ELSE 0 END), 0) - Isnull(Sum(CASE WHEN MONTH = '2013-8-1' THEN ScrapDiscarded ELSE 0 END), 0) as Scrap,
    SUM(CASE WHEN Month = '2013-8-1' THEN WaitingForApproval ELSE 0 END) as WFA  
from 
    Instock
where 
    Vendor = 'abc'

问题是需要包含的最后一个查询。它从 OutStock table 获取数据，但我想在上面的查询中包含该查询，以便它 returns 作为单行结果。我能够使用嵌套查询满足要求，但我希望使用 条件聚合 获得相同的结果以实现数据库性能平滑。

需要包含的查询是：

select 
    COUNT(Product) as Despatched 
from 
    OutStock 
where 
    DispatchDate between '2013-8-1' and '2014-2-1' 
    and Vendor = 'abc'`

所以将两者结合起来我想作为一个查询执行，它将 return 一行

Answer 1

只需将第二个查询添加到第一个查询的列列表中，因为它只会 return 一行。试试这个。

SELECT Sum(CASE
             WHEN MONTH = '2013-8-1' THEN CurrentStock
             ELSE 0
           END)                                 AS CurrentStock,
       Isnull(Sum(CASE WHEN MONTH = '2014-2-1' THEN CPU ELSE 0 END), 0) - 
       Isnull(Sum(CASE WHEN MONTH = '2013-8-1' THEN CPU ELSE 0 END), 0) AS CPU,
       Sum(CASE WHEN Month = '2013-8-1' THEN NonCPUWIP ELSE 0 END) AS NonCPU,
       Isnull(Sum(CASE WHEN MONTH = '2014-2-1' THEN ScrapDiscarded ELSE 0 END), 0) - 
       Isnull(Sum(CASE WHEN MONTH = '2013-8-1' THEN ScrapDiscarded ELSE 0 END), 0)AS Scrap,
       Sum(CASE WHEN Month = '2013-8-1' THEN WaitingForApproval ELSE 0 END) AS WFA,
       (SELECT Count(STBSerialNUMBER)
        FROM   OutStock
        WHERE  DispatchDate BETWEEN '2013-8-1' AND '2014-2-1'
                AND Vendor = 'abc' ) as Despatched
FROM   Instock I
WHERE  Vendor = 'abc'

更新：

如果您想要每个模型的结果计数，请将 subquery 转换为 correlated subquery。应该是这样的

  (SELECT Count(STBSerialNUMBER)
   FROM   OutStock O
   WHERE o.model = i.model  -- here is the change
   AND O.DispatchDate BETWEEN '2013-8-1' AND '2014-2-1'
   AND o.Vendor = 'abc')

此处对于 Instock table 中的每个 model，将计算 outstock 中的相应 count。

或者您也可以使用Left Join。先计算Outstocktablejoin中每个model的个数，结果返回给Instocktable使用模型

   ....
   From Instock I Left Join 
   (SELECT Count(STBSerialNUMBER) OutStock_count,Model
   FROM   OutStock O
   WHERE  O.DispatchDate BETWEEN '2013-8-1' AND '2014-2-1'
   AND o.Vendor = 'abc'
   Group by Model) O on o.model = i.model

在 SQL Server 2008 中使用条件聚合

Using Conditional Aggregate in SQL Server 2008

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