From: | Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> |
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To: | tgl(at)sss(dot)pgh(dot)pa(dot)us (Tom Lane), Dimitri Fontaine <dfontaine(at)hi-media(dot)com>, hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Range types |
Date: | 2009-12-17 15:55:27 |
Message-ID: | 87my1hlizp.fsf@news-spur.riddles.org.uk |
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Lists: | pgsql-hackers |
>>>>> "Tom" == Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
Someone mentioned LATERAL?
>> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>>> 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);
Tom> I don't think that does it. Maybe I misunderstand LATERAL, but
Tom> what that looks like to me is that each p1 will be separately
Tom> filtered by each p2, giving rise to a distinct element in the
Tom> output. What we need is for each p1 to be filtered by *all*
Tom> p2's, successively (though in any order).
Right, that's not a job for LATERAL, though it could be done easily
enough in one statement with a recursive CTE, I think.
--
Andrew (irc:RhodiumToad)
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