Tom Lane <t...@sss.pgh.pa.us> writes:
> Dimitri Fontaine <dfonta...@hi-media.com> writes:
>> Tom Lane <t...@sss.pgh.pa.us> writes:
>>> foreach p2_member in unnest(p2) loop
>>> p1 := array(select period_except(p1_member, p2_member)
>>> from unnest(p1) p1_member);
>>> end loop;
>>>
>>> But maybe it can be done in a single SQL command.
>
>> Yeah, as soon as you have LATERAL, I think. Without it there's no way to
>> compose SRF in SQL, AFAIK.
>
> Hm, how would you do it with LATERAL? The problem is not so much
> composition as the need for a variable number of rounds of
> composition.
Let's have a try at it:
select p2_member, array_accum(p1)
from unnest(p2) as p2_member
lateral (select period_except(p1_member, p2_member)
from unnest(p1) p1_member) as x(p1);
I'm not sure I understand how the explicit looping over unnest(p2) is different
from using lateral, or even if that's what you're talking about when
mentioning variable number of rounds.
Regards,
--
dim
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