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

On 2016-09-02 10:20:42 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On 2016-09-02 09:05:35 -0500, Kevin Grittner wrote:
> >>> In general, we've been skeptical about giving any guarantees about
> >>> result ordering.
>
> > Well, it's historically how we behaved for SRFs. I'm pretty sure that
> > people will be confused if
> > SELECT generate_series(1, 10) FROM sometbl;
> > suddenly returns rows in an order that reverse from what
> > generate_series() returns.
>
> True, but how much "enforcement" do we need really? This will be a cross
> product join, which means that it can only be done as a nestloop not as a
> merge or hash (there being no join key to merge or hash on). ISTM all we
> need is that the SRF be on the inside of the join, which is automatic
> if it's LATERAL.

Right. But there's nothing to force a lateral reference to be there
intrinsically. I've added a "fake" lateral reference to the ROWS FROM
RTE to the subquery, when there's none otherwise, but that's not
entirely pretty. I'm inclined to go with that though, unless somebody
has a better idea.

Greetings,

Andres Freund