The primary problem was that the update command doesn't modify rows in the
order u want to do it.
I think the update starts with the latest inserted rows. I guess.
Anyway, in real life this update modifies only one row with a value wich is
diff of null.
It was really handy if it was specified the option ORDER for the update
command.
----- Original Message -----
From: "Greg Stark" <gsstark@mit.edu>
To: "Viorel Dragomir" <bigchief@vio.ro>
Cc: <pgsql-sql@postgresql.org>
Sent: Tuesday, July 15, 2003 5:55 PM
Subject: Re: [SQL] summing tables
>
> 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
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Don't 'kill -9' the postmaster