I have a table foo (d,f,mj,mn) where (d,f) is the primary unique key and the only index. I've added a new sequence and a new integer column v and would like to insert into v using this new sequence but using the sort order of (mj,mn) instead of (d,f), which is how it's working if I do a simple "update foo set v = nextval('inc')". What's the best way to accomplish this ?