sql - 如何聚合表达式的结果？

Question

在调整 docBal 后，我试图获得每家公司的总和（docBal）。但是当我运行下面的查询时，我被迫在 groupby 中包含 doctype 和 docbal——这是我不想要的。如何修改此查询？

 select 
  DocBal =  CASE d.DocType WHEN 'AD' THEN -d.DocBal
                           ELSE d.DocBal END,
  Sum(DocBal)
  from Vendor v
   inner join APDoc d
   on v.VendId = d.VendId
   where 
      d.PerPost = 201307
      and d.DocType in ('VO','AP','AD')
      and d.OpenDoc = 1
      and Acct = 210110
     group by CpnyID

Answer 1

您可以使用子选择来捕获您需要的信息。

    SELECT  S.CpnyID,
            SUM(S.DocBal)
    FROM    (
            SELECT  CpnyID,
                    CASE d.DocType WHEN 'AD' THEN -d.DocBal ELSE d.DocBal END AS DocBal
            FROM    Vendor v
                    INNER JOIN APDoc d ON v.VendId = d.VendId
            WHERE     d.PerPost = 201307
            AND d.DocType in ('VO','AP','AD')
            AND d.OpenDoc = 1
            AND Acct = 210110
    ) AS S
    GROUP BY S.CpnyID

这应该为您提供所需的数据，而不必在聚合函数中包含其他列。

Answer 2

您不是在说您使用的是什么 SQL 产品（以及哪个版本）。确实，其他人建议的派生表解决方案适用于任何产品，但如果您使用的是 SQL Server 2005 或更高版本，您也可以使用 CROSS APPLY，如下所示：

SELECT
  CpnyID,  -- assuming you would like to know which SUM() belongs to which CpnyID
  SUM(x.DocBal)
FROM Vendor AS v
INNER JOIN APDoc AS d ON v.VendId = d.VendId
CROSS APPLY (
  SELECT DocBal = CASE d.DocType WHEN 'AD' THEN -d.DocBal ELSE d.DocBal END
) AS x
WHERE d.PerPost = 201307
  AND d.DocType in ('VO','AP','AD')
  AND d.OpenDoc = 1
  AND Acct = 210110
GROUP BY
  CpnyID
;

在我看来，还有一个更简单的解决方案：您可以将整个 CASE 表达式作为 SUM 的参数，如下所示：

SELECT
  CpnyID,
  SUM(CASE d.DocType WHEN 'AD' THEN -d.DocBal ELSE d.DocBal END)
FROM Vendor AS v
INNER JOIN APDoc AS d ON v.VendId = d.VendId
WHERE d.PerPost = 201307
  AND d.DocType in ('VO','AP','AD')
  AND d.OpenDoc = 1
  AND Acct = 210110
GROUP BY
  CpnyID
;

Answer 3

select sum(DocBal) FROM
(select 
  DocBal =  CASE d.DocType WHEN 'AD' THEN -d.DocBal
                           ELSE d.DocBal END,
  CpnID
  from Vendor v
   inner join APDoc d
   on v.VendId = d.VendId
   where 
      d.PerPost = 201307
      and d.DocType in ('VO','AP','AD')
      and d.OpenDoc = 1
      and Acct = 210110) a
GROUP BY CpnID

Answer 4

    select sum(DocBal) from (
        select 
          DocBal =  CASE d.DocType WHEN 'AD' THEN -d.DocBal
                                   ELSE d.DocBal END,
          CpnyID
          from Vendor v
           inner join APDoc d
           on v.VendId = d.VendId
           where 
              d.PerPost = 201307
              and d.DocType in ('VO','AP','AD')
              and d.OpenDoc = 1
              and Acct = 210110
      )
  group by CpnyID