Use of GROUP BY twice in MySQL

Question

My table looks like this.

Location    Head    Id  IntTime
1           AMD     1   1
2           INTC    3   3
3           AMD     2   2
4           INTC    4         


        

Answer 1

If I understand correctly, you want the rows that have the smallest int/time values by head and id. I am not seeing what the second "group by head" is getting you.

The following does what I think you want:

select t.*
from t join
     (select head, id, min(intTime) as min_intTime
      from t
      group by head, id
     ) tsum
     on tsum.head = t.head and
        tsum.id = t.id and
        tsum.min_intTime = t.intTime

You might just want the smallest intTime for all "head" values. If so, the query looks like:

select t.*
from t join
     (select head, min(intTime) as min_intTime
      from t
      group by head
     ) tsum
     on tsum.head = t.head and
        tsum.min_intTime = t.intTime