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

Andres Freund <andres@anarazel.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 betweenSELECT a, b FROM ... ORDER BY srf();
andSELECT 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