Suppose if my Input is:
ID GroupID Qty 1 1 100 2 1 200 3 1 300 4 2 98 5 2 198 6 3 175 7 3 27
EDIT
SELECT MIN(ID) , GroupID, (SELECT TOP 1 Qty FROM @TABLE T2 WHERE T2.ID = MIN(T1.ID)) FROM @TABLE T1 GROUP BY GroupID
Input
ID GroupID Qty 1 1 100 2 1 200 3 1 300 4 2 98 5 2 198 6 3 175 7 3 275 8 3 375 9 4 215
Output
1 1 100 4 2 98 6 3 175 9 4 215