Re: window function and order by

=?ISO-8859-1?Q?Torsten_F=F6rtsch?= <torsten(dot)foertsch(at)gmx(dot)net> writes:
> select id, buy_price, sum(buy_price) over (order by id) sum
> from fmb
> where 202300<=id and id<=202400
> order by id;

> Do I need the ORDER BY clause at the end? Or does the ORDER BY in the
> window function already define the order of the result set?

According to the standard, you'd need the ORDER BY to guarantee any
particular ordering of the output. However, our implementation will
deliver the rows in the window function's order as long as there's
only one window function order (otherwise you get a more-or-less-
random one of them...). It won't cost anything to have the ORDER BY
though, so I'd recommend keeping it.

regards, tom lane