Re: Implement targetlist SRFs using ROWS FROM() (was Changed SRF in targetlist handling)

Andres Freund <andres(at)anarazel(dot)de> writes:
> 0002-Shore-up-some-weird-corner-cases-for-targetlist-SRFs.patch
> Forbid UPDATE ... SET foo = SRF() and ORDER BY / GROUP BY containing
> SRFs that would change the number of returned rows. Without the
> latter e.g. SELECT 1 ORDER BY generate_series(1,10); returns 10 rows.

I'm on board with disallowing SRFs in UPDATE, because it produces
underdetermined and unspecified results; but the other restriction
seems 100% arbitrary. There is no semantic difference between
SELECT a, b FROM ... ORDER BY srf();
and
SELECT a, b, srf() FROM ... ORDER BY 3;
except that in the first case the ordering column doesn't get returned to
the client. I do not see why that's so awful that we should make it fail
after twenty years of allowing it. And I certainly don't see why there
would be an implementation reason why we couldn't support it anymore
if we can still do the second one.

regards, tom lane