From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
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To: | jonathan vanasco <postgres(at)2xlp(dot)com> |
Cc: | pgsql-general general <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: why isn't this subquery wrong? |
Date: | 2017-04-20 22:42:06 |
Message-ID: | CAKFQuwbecWp41+hxyeL8qxmtuu4S6bN2XNpw8_AOkWUCzu8PDg@mail.gmail.com |
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Lists: | pgsql-general |
On Thu, Apr 20, 2017 at 3:17 PM, jonathan vanasco <postgres(at)2xlp(dot)com> wrote:
> postgres doesn't raise an error because example_a__data does have a bar_id
> -- but example_a__rollup doesn't and there's no explicit correlation in the
> query.
>
>
Subqueries can see all columns of the parent. When the subquery actually
uses one of them it is called a "correlated subquery".
See another recent question on this topic for more details:
https://www.postgresql.org/message-id/20160714135233.1410.92538%40wrigleys.postgresql.org
Unfortunately at present everyone here seems content answering this on the
list semi-frequently instead of updating the docs and/or FAQ section of our
wiki. The topic is covered (I think...) but not easily found (I failed to
just now...) - and harder when you don't know what to call it in the first
place.
David J.
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