SQL選擇列的最大值的行（在GROUP BY中有兩個字段）

Question

這是我的基本查詢（SQL Server）：

SELECT projectID, businessID, sum(number) AS summ
FROM table
GROUP BY projectID, businessID
ORDER BY projectID, sum(number) DESC

它產生一個像這樣的表：

         Project ID      Business ID    Summ
              1              1           63
              1              2           32 
              1              3            6
              2              3           45
              2              1           44
              2              2            3

我想獲取項目ID和業務ID，其中Summ列對於每個項目ID最大。 所以給出的例子中的第1行和第4行。 我如何調整原始查詢來執行此操作？

Answer 1

如果您可能有關聯並希望返回兩行，則應使用：

select * from
    (select projectID, businessID
      , sum(number) as Tot
      , max(sum(number)) over (partition by projectID) as MSum
      from Table
    group by projectID, businessID)
a
where a.tot = a.Msum

Answer 2

您可以使用分析函數：

SELECT projectID,
       businessID,
       summ
  FROM(SELECT projectID,
              businessID,
              SUM(number) AS summ,
              ROW_NUMBER() OVER (PARTITION BY projectID
                                     ORDER BY SUM(number) DESC) AS rn
        FROM table
       GROUP
          BY projectID,
             businessID
      ) t
 WHERE rn = 1
 ORDER
    BY projectID;

希望有所幫助。

Answer 3

您需要第二個聚合或分析功能。 這是使用第二個聚合執行此操作的方法：

WITH sums as (
  SELECT projectID, businessID, sum(number) AS summ
  FROM table
  GROUP BY projectID, businessID
)
SELECT sums.projectId, sums.businessId, sums.summ
FROM
  (
    SELECT projectID, MAX(summ) as ms
    FROM sums
    GROUP BY projectID
  ) ms
  JOIN sums
    ON sums.projectId = ms.projectId AND sums.summ = ms.ms

您需要在不支持分析功能的系統上使用此方法，幸運的是，它不包括SQL Server。