Take the result of a MySQL query and put in another query

Question

7I have a table named "Critères"

Critères have two columns:

"Prestation / Code hors projet" - "Heures"

Salut                    20
Salut                    42
Salut                    35
Coco                     152
Coco                     -52
Lolilol                  89

I just need to have this result IN THE SAME TABLE:

"Prestation / Code hors projet" - "Heures"

Salut                    97
Coco                     100
Lolilol                  89

Is this clear ?

Please I really need help

I have this query for the moment: "SELECT Prestation / Code hors projet, SUM(Heures) FROM Critères GROUP BY Prestation / Code hors projet"

The problem is that I don't know what to do with the results =/

Regards,