How to do UPDATE with GROUP BY

[MM]

I'm using Oracle database.

It is true that I can't use update when I have group by ?

For example I tried with:

update (select t1.ID, sum(t1.quantity ) as quantity, max(t2.out) as out
from t1, t2

where

t1.id=t2.ID and
GROUP BY s01.sklbr) temp

set tem.out=temp.ou t- temp.quantity



And get error:ORA:01732 "Data manipulation operation not legal on this view"



I suppose that I can do with procedure and cursor but I don't know how. Can
anybody help me?



Thanks a lot MM