Question

I have exhausted my wit with this problem, so I bring the challenge to you:

--CREATING DATA:

DECLARE @CONTACTS TABLE (ID INT, NickName CHAR(10))
INSERT INTO @CONTACTS VALUES (1359,'John Smith')
INSERT INTO @CONTACTS VALUES (1360,'Ana Keller')
INSERT INTO @CONTACTS VALUES (1361,'Joshua Doe')

DECLARE @ENTERPRISES TABLE (ID INT, CON_ID INT, ASSOCIATION DATETIME)
INSERT INTO @ENTERPRISES VALUES (123,1359,Convert(datetime, '2000-10-09', 120))
INSERT INTO @ENTERPRISES VALUES (123,1360,Convert(datetime, '2000-02-21', 120))
INSERT INTO @ENTERPRISES VALUES (123,1361,Convert(datetime, '2000-04-09', 120))

--QUERYING THE DATA:
SELECT * FROM @CONTACTS C
JOIN @ENTERPRISES E ON C.ID = E.CON_ID

--THE RESULT SET OF MY DREAMS:
    1359    John Smith    123    1359    2000-10-09

What I want is an entire row of the query before, but only the one that has the maximum ASSOCIATION date for each Enterprise ID. This is only an example for the sake of clarity, my real query is much more complex, with much more columns and trillions of rows. I have tried

SELECT *,max(FOUNDING) OVER (PARTITION BY E.ID) FROM @CONTACTS C
JOIN @ENTERPRISES E ON C.ID = E.CON_ID

But it still brings all three rows. Other approaches were worse and led to the parser asking me to GROUP BY every column. I appreciate your help.

Answer 1

WITH cteMaxAssociation AS (
    SELECT ID, CON_ID, ASSOCIATION,
           ROW_NUMBER() OVER(PARTITION BY ID ORDER BY ASSOCIATION DESC) AS RowNum
        FROM @ENTERPRISES
)
SELECT C.ID, C.NickName, ma.ID, ma.CON_ID, ma.ASSOCIATION
    FROM @CONTACTS C
        INNER JOIN cteMaxAssociation ma
            ON C.ID = ma.CON_ID
                AND ma.RowNum = 1