Question

我已经尝试了几个小时但是无法使用DB2来执行查询以执行我想要的操作。从表公司和用户我有每个公司/用户的以下票证数量信息

user         company      quantity
------------ ------------ ------------
mark         nissan       300
tom          toyota       50
steve        krysler      80
mark         ford         20
tom          toyota       120
jose         toyota       230
tom          nissan       145
steve        toyota       10
jose         krysler      35
steve        ford         100

这是由查询生成的：

SELECT T.USER, COUNT(T.USER) AS QUANTITY, T.COMPANY FROM TICKET T
INNER JOIN COMPANY P ON P.COMPANY = T.COMPANY 
GROUP BY (T.USER, T.COMPANY) -- ORDER BY QUANTITY DESC

我想看到的是每家公司的最高用户，因此根据上述数据，查询应该显示给我：

user         company      quantity (Top user per company)
------------ ------------ --------------------------------
mark         nissan       300
jose         toyota       230
steve        ford         100
steve        krysler      80

如何编写SQL以返回此结果？

最终答案（在评论中注明）：

SELECT user, quantity, company
  FROM (SELECT user, quantity, company,
               RANK () OVER (PARTITION BY company ORDER BY quantity DESC) AS r
          FROM (SELECT T.USER, COUNT(T.USER) AS QUANTITY, T.COMPANY
                  FROM TICKET T JOIN COMPANY P ON P.COMPANY = T.COMPANY
                 GROUP BY (T.USER, T.COMPANY) ) s ) t
 WHERE r = 1;

Answer 1

逐步建立起来。

找出每家公司的最大数量，假设问题中显示的第一个数据表被调用＆＃39;门票＆＃39;：

SELECT Company, MAX(Quantity) AS MaxQuantity
  FROM Tickets
 GROUP BY Company;

现在，找到该公司具有该最大数量的用户的数据：

SELECT T.User, T.Company, M.MaxQuantity
  FROM Tickets AS T
  JOIN (SELECT Company, MAX(Quantity) AS MaxQuantity
          FROM Tickets
         GROUP BY Company) AS M
    ON T.Company = M.Company AND T.Quantity = M.MaxQuantity;

如果特定公司的最高数量是200，而且该公司的两个用户都获得了200，那么此查询会列出两个用户。

现在，如果你的意思是你在问题中显示的查询生成了第一个结果表，那么我在上面调用的票证需要是派生表：

SELECT T.User, COUNT(T.User) AS Quantity, T.Ccompany
  FROM Ticket AS T
 INNER JOIN Company AS P ON P.Company = T.Company 
 GROUP BY (T.User, T.Company)
 ORDER BY QUANTITY DESC

在这种情况下，我们可以使用WITH子句（语法未经检查，但我认为每个SQL标准都是正确的）：

WITH Tickets AS
    (SELECT T.User, COUNT(T.User) AS Quantity, T.Ccompany
       FROM Ticket AS T
       JOIN Company AS P ON P.Company = T.Company 
      GROUP BY (T.User, T.Company)
    )
SELECT T.User, T.Company, M.MaxQuantity
  FROM Tickets AS T
  JOIN (SELECT Company, MAX(Quantity) AS MaxQuantity
          FROM Tickets
         GROUP BY Company) AS M
    ON T.Company = M.Company AND T.Quantity = M.MaxQuantity;

显然，如果您愿意，也可以将WITH子查询写出两次。

Answer 2

这应该有效。创建派生视图以计算每个用户和每个公司的数量。然后获取最大值然后数量，然后将最大值加回到数量的计算。

SELECT p.company, 
       t.user, 
       t.quantity 
FROM   (SELECT MAX(t.quantity) max_quantity, 
               t.company 
        FROM   (SELECT  
                       COUNT(t.user) quantity, 
                       t.company 
                FROM   ticket t 
                GROUP  BY t.company) t) maxq 
       INNER JOIN (SELECT t.user, 
                          t.company, 
                          COUNT(t.user) quantity 
                   FROM   ticket t 
                   GROUP  BY t.company, 
                             t.user) t 
         ON maxq.max_quantity = t.quantity 
            AND maxq.company = t.company 
       INNER JOIN company p 
         ON p.company = t.company 
ORDER  BY t.quantity DESC

按标签显示StackOverflow数据的最高用户的工作示例可以是found here。

Top Group By DB2

2 个答案: