From: Tom Lane <tgl@sss.pgh.pa.us>
To: Josh Berkus <josh@agliodbs.com>
cc: Tim Dudgeon <tdudgeon.ml@gmail.com>, pgsql-sql@postgresql.org,
 pgsql-performance@postgresql.org
Subject: Re: Re: [SQL] querying with index on jsonb slower than standard
 column. Why?
In-reply-to: <548B5CF4.4030009@agliodbs.com>
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 <27877.1418057764@sss.pgh.pa.us> <3936.1418071989@sss.pgh.pa.us>
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Comments: In-reply-to Josh Berkus <josh@agliodbs.com>
 message dated "Fri, 12 Dec 2014 13:24:04 -0800"
Date: Fri, 12 Dec 2014 16:44:10 -0500
Message-ID: <8867.1418420650@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-performance-owner@postgresql.org

Josh Berkus <josh@agliodbs.com> writes:
> Yeah, I believe the core problem is that Postgres currently doesn't have
> any way to have variadic return times from a function which don't match
> variadic input types.  Returning a value as an actual numeric from JSONB
> would require returning a numeric from a function whose input type is
> text or json.  So a known issue but one which would require a lot of
> replumbing to fix.

Well, it'd be easy to fix if we were willing to invent distinct operators
depending on which type you wanted out (perhaps ->> for text output as
today, add ->># for numeric output, etc).  Doesn't seem terribly nice
from a usability standpoint though.

The usability issue could be fixed by teaching the planner to fold a
construct like (jsonb ->> 'foo')::numeric into (jsonb ->># 'foo').
But I'm not sure how we do that except in a really ugly and ad-hoc
fashion.

			regards, tom lane


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