From: | David Fetter <david(at)fetter(dot)org> |
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To: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
Cc: | James Coleman <jtc331(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Floris Van Nee <florisvannee(at)optiver(dot)com>, Rafia Sabih <rafia(dot)pghackers(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Bhushan Uparkar <bhushan(dot)uparkar(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> |
Subject: | Re: Index Skip Scan |
Date: | 2019-07-04 00:41:18 |
Message-ID: | 20190704004118.GB24679@fetter.org |
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Lists: | pgsql-hackers |
On Thu, Jul 04, 2019 at 10:06:11AM +1200, David Rowley wrote:
> On Thu, 4 Jul 2019 at 09:02, James Coleman <jtc331(at)gmail(dot)com> wrote:
> > I think that example is the opposite direction of what David (Rowley)
> > is saying. Unique on {a, b} implies unique on {a, b, c} while you're
> > correct that the inverse doesn't hold.
> >
> > Unique on {a, b} also implies unique on {b, a} as well as on {b, a, c}
> > and {c, a, b} and {c, b, a} and {a, c, b}, which is what makes this
> > different from pathkeys.
>
> Yeah, exactly. A superset of the unique columns is still unique.
Thanks for clarifying!
Best,
David.
--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
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