Re: lateral function as a subquery - WIP patch

On Sat, Mar 10, 2012 at 4:16 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> 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.

True. I just meant that no join filter was implied.

--
Robert Haas
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