"Viorel Dragomir" <bc@vio.ro> writes:
> 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.
Are you hoping to produce a running total? That's very difficult in standard
SQL. That would be very different from the query you asked for.
Running totals, ranking, lead/lag, are all things that are very difficult to
do in standard SQL. They don't fit in the unordered set model that SQL follows
so doing them without special non-standard functions is very hard and
inefficient.
The functions to do them don't fit well within the SQL universe either, which
might be why they don't exist yet in postgres.
--
greg
