Good afternoon,   I'll try to answer to all of you.   1) I have found a solution earlier. I just needed to make some calculations to check if it made sense. Actually I ended up using a similar technique as Tom (the proc sql one), and then if needed I can use a left join (avoiding to update allows me to also avoid the subquery, which took so long). By the way, there is no specific reason for SQL, I just do not know how to use SAS (excepted for a few procedures).   2) For AMSAS and PaigeMiller : thank you too for your help. Actually I'm not used to post questions, therefore I thought it was clear that C1... C6 meant "column number 1, 2, ... 6" (but have different names). Sorry if it was not clear, I will try to be more explicite in the future.   3) for ballardw : thank you for those precisions. Yes as you guessed, no negative values possible in my case (however, for a more general case, it would be dangerous). ... View more