Re: lateral function as a subquery - WIP patch

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Fri, Mar 9, 2012 at 8:15 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Um ... how do you get the subquery result rows to join to only the
>> correct rows of the other tables? This looks like an unconstrained join
>> to me, which is not what I believe the SQL spec for LATERAL to be, and
>> it doesn't seem especially useful either. (If a subquery could do what
>> people wanted, we'd not be hearing all the requests for LATERAL.)

> I think LATERAL is intended as more or less an unconstrained nested
> loop with the lateral expression on the inner side, parameterized by
> value from the outer side. Typically it's a SRF.

Um ... if it's parameterized by values from a "current row" of the outer
side, then it's not an unconstrained join. That would be like doing an
inner indexscan join and producing a cross-join result.

regards, tom lane