| From: | Andy Fan <zhihui(dot)fan1213(at)gmail(dot)com> |
|---|---|
| To: | David Rowley <dgrowleyml(at)gmail(dot)com> |
| Cc: | Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, florisvannee(at)optiver(dot)com, pg(at)bowt(dot)ie, jesper(dot)pedersen(at)redhat(dot)com, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, jtc331(at)gmail(dot)com, rafia(dot)pghackers(at)gmail(dot)com, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, 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: | 2020-03-11 03:44:23 |
| Message-ID: | CAKU4AWqqsagFb=J4bu5YfxokZvmqb_hGDZFtimfSzNLBFthUuQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
>
>
> I think the UniqueKeys may need to be changed from using
> EquivalenceClasses to use Exprs instead.
>
When I try to understand why UniqueKeys needs EquivalenceClasses,
see your comments here. I feel that FuncExpr can't be
used to as a UniquePath even we can create unique index on f(a)
and f->strict == true. The reason is even we know a is not null,
f->strict = true. it is still be possible that f(a) == null. unique index
allows more than 1 null values. so shall we move further to use varattrno
instead of Expr? if so, we can also use a list of Bitmapset to present
multi
unique path of a single RelOptInfo.
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