Sql query to return one single record per each combination in a table

Question

I need the result for every combination of (from_id, to_id) which has the minimun value and the loop matching a criteria.

So basically I need the loop that has the minim

Answer 1

As I understand the problem this will work:

SELECT  t.value, t.from_id, t.to_id, t.loop_id
FROM    MyResults t
        INNER JOIN
        (   SELECT  From_ID, To_ID, MIN(Value) [Value]
            FROM    MyResults
            WHERE   Loop_ID % 2 = 0
            GROUP BY From_ID, To_ID
        ) MinT
            ON MinT.From_ID = t.From_ID
            AND MinT.To_ID = t.To_ID
            AND MinT.Value = t.Value

However, if you had duplicate values for a From_ID and To_ID combination e.g.

value     from_id   to_id     loop_id
-------------------------------------

0.1         A         B          2

0.1         A         B          4

This would return both rows.

If you are using SQL-Server 2005 or later and you want the duplicate rows as stated above you could use:

SELECT  Value, From_ID, To_ID, Loop_ID
FROM    (   SELECT  *, MIN(Value) OVER(PARTITION BY From_ID, To_ID) [MinValue]
            FROM    MyResults
        ) t
WHERE   Value = MinValue

If you did not want the duplicate rows you could use this:

SELECT  Value, From_ID, To_ID, Loop_ID
FROM    (   SELECT  *, ROW_NUMBER() OVER(PARTITION BY From_ID, To_ID ORDER BY Value, Loop_ID) [RowNumber]
            FROM    MyResults
        ) t
WHERE   RowNumber = 1