Re: Index Skip Scan

From: David Fetter <david(at)fetter(dot)org>
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
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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!

David Fetter <david(at)fetter(dot)org>
Phone: +1 415 235 3778

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