How to get first record out of each group from the result retrieved by using group by command

Question

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         


        

Answer 1

The best and more flexible way in my opinion would be to use ROW_NUMBER(). The below I've tested for your example, just replace tmpTable with your table name:

SELECT a.* FROM tmpTable a INNER JOIN 
(SELECT    ROW_NUMBER() over(PARTITION BY GroupID ORDER BY ID, GroupID) AS SEQ, tmpTable.*
FROM            tmpTable) b
ON a.ID = b.ID AND a.GroupID = b.GroupID
WHERE b.SEQ = 1

read more about how to use ROW_NUMBER: https://docs.microsoft.com/en-us/sql/t-sql/functions/row-number-transact-sql