--
-- "FIRST" equivalents
--

-- Test table
DECLARE @T 
TABLE   (
        group_id    INTEGER NOT NULL, 
        subgroup    INTEGER NOT NULL,
        
        PRIMARY KEY (group_id, subgroup)
        );

-- Sample data from Flo
INSERT  @T
        (group_id, subgroup)
SELECT  1, 11   UNION ALL
SELECT  1, 12   UNION ALL
SELECT  1, 13   UNION ALL
SELECT  2, 21   UNION ALL
SELECT  2, 22   UNION ALL
SELECT  2, 23   UNION ALL
SELECT  3, 31   UNION ALL
SELECT  3, 32;

-- Solution by Flo
SELECT  group_id,
        MIN(subgroup)
FROM    @t
GROUP   BY 
        group_id
ORDER   BY
        group_id;
   
-- Solution by G2
SELECT  T1.group_id,
        T1.subgroup
FROM    (
        SELECT  group_id,
                subgroup,
                rn =    ROW_NUMBER() 
                        OVER (
                        PARTITION BY group_id
                        ORDER BY subgroup)
        FROM    @T T1
        ) T1
WHERE   T1.rn = 1
ORDER   BY
        T1.group_id;

-- "Segment Top" solution
SELECT  T1.group_id,
        T1.subgroup
FROM    @T T1
WHERE   T1.subgroup =
        (
        SELECT  MIN(subgroup)
        FROM    @T T2
        WHERE   T2.group_id = T1.group_id
        )
ORDER   BY
        T1.group_id;

-- APPLY TOP solution
SELECT  T1.group_id,
        iTVF.subgroup
FROM    (
        SELECT  DISTINCT group_id
        FROM    @T T
        ) T1
CROSS
APPLY   (
        SELECT  TOP (1)
                T2.subgroup
        FROM    @T T2
        WHERE   T2.group_id = T1.group_id
        ORDER   BY
                T2.group_id
        ) iTVF
ORDER   BY
        T1.group_id;