To solve this problem efficiently you probably need the lead/lag analytic
functions. Unfortunately Postgres doesn't have them.
You could do it with something like:
update foo set c = a+b+(select c from foo as x where seq < foo.seq ORDER BY seq desc LIMIT 1)
or the more standard but likely to be way slower:
update foo set c = a+b+(select c from foo as x where seq = (select max(seq) from foo as y where seq < foo.seq))
However, i would suggest that if you have an implicit relationship between
records you should make that relationship explicit with a foreign key. If you
had a column that contained the seq of the parent record then this would be
easy. I'm really puzzled how this query as currently specified could be
useful.
--
greg
