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Question

I\'ve been trying for hours but can\'t get the query to do what I want using DB2. From table Company and Users I have the following tickets quantity info per company/user

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Answer 1

This should work. Create a derived view to calculate the Quantity per user and per company. Then get the max of then Quantity and then join the max back to the the calculation of the quantity.

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 

A working sample that shows the top users by tag for the StackOverflow data can be found here.

Answer 2

Build it up step by step.

Find the maximum quantity for each company, assuming the first data table shown in the question is called 'Tickets':

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

Now, find the data for the user(s) with that maximum quantity for that 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;

If the top quantity for a particular company was, say, 200 and two users both scored 200 for that company, then this query lists both users.

Now, if you mean that the query you show in the question generates the first result table, then what I called tickets just above needs to be the derived table:

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 

In which case, we can use a WITH clause (syntax unchecked, but I think it is correct per SQL standard):

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;

Clearly, you can also write the WITH sub-query out twice if you prefer.