Question

I have a table which represents a “Contract” between two rows in another table. Given the data below, how can I get the most common Distributer for each EndUser?

Contracts

EndUserId | DistributerId | StartDate | EndDate 
-----------------------------------------
1         | 8             | ...       | ...
1         | 9             | ...       | ...
1         | 9             | ...       | ...
2         | 8             | ...       | ...
2         | 8             | ...       | ...
2         | 9             | ...       | ...   
3         | 8             | ...       | ...   
3         | 9             | ...       | ...   

The query I’m after must return the following:

EndUserId | DistributerId
-------------------------
1         | 9
2         | 8
3         | 8 or 9, it is of no consequence.

Thanks in advance! Searching hasn’t been much help here because it’s hard to describe the goal without sample data etc.

Answer 1

Untested, but I think this will do it:

WITH ContractCounts AS 
( --First Get the counts for each distributer
  SELECT EndUserID, DistributerID, Count(*) As ContractCount
  FROM Contracts
  GROUP BY EndUserID, DistributerID
),
ContractMax AS 
(  -- Then find out how many contracts the largest distributed for each user had
  SELECT EndUserID, Max(ContractCount) As MaxContractCount
  FROM ContractCounts 
  GROUP BY EndUserID
)
-- and finally select only the distributor for each user who's count matches the prior query
SELECT c.EndUserID, MAX(c.DistributerID) AS DistributerID
FROM ContractCounts c
INNER JOIN ContractMax m on m.EndUserID=c.EndUserID AND c.ContractCount = m.MaxContractCount
GROUP BY c.EndUserID