Date: Thu, 9 Aug 2018 10:14:33 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Morgan Owens <packrat@varteg.nz>
Cc: Nick Farmer <farmernick-pg@varteg.nz>, pgsql-docs@lists.postgresql.org
Subject: Re: Parameter types are inferred from context of first use only.
Message-ID: <20180809141433.GA2876@momjian.us>
References: <153233728858.1404.15268121695358514937@wrigleys.postgresql.org>
 <20180808172444.GC2611@momjian.us>
 <424fb120-8761-89e3-b538-fcc78d95aae9@varteg.nz>
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On Thu, Aug  9, 2018 at 12:18:27PM +1200, Morgan Owens wrote:
> On 2018-08-09 05:24, Bruce Momjian wrote:
> >On Mon, Jul 23, 2018 at 09:14:48AM +0000, PG Doc comments form wrote:
> >>The following documentation comment has been logged on the website:
> >>
> >>Page: https://www.postgresql.org/docs/10/static/sql-prepare.html
> >>Description:
> >>
> >>Background can be found on the bugs list (pgsql-bug #15289). It was
> >>explained that when a prepared statement parameter needs to have its type
> >>inferred then, should the parameter be used more than once, only the first
> >>use is considered. (The example in that report is that the type of $1 can be
> >>inferred from "($1 = col) or ($1 is null)" but not from "($1 is null) or ($1
> >>= col)".)
> >>
> >>The documentation as it stands says only that the parameter's type is
> >>inferred from the context in which it is used. The "first use only" proviso
> >>is not mentioned (hence "context" isn't so broad as to consist of all of the
> >>expressions in which the parameter appears).
> >
> >I have developed the attached patch to cover what you found.
> >
> 
> That says it for me. The third mention of context doesn't need anything
> because it's referring specifically to the (single) use of $2 in the
> example. I have to presume the type inference happens before any structural
> changes that might change the meaning of "first occurrence".

Great, patch applied through 9.3.  I also changed "used" to
"referenced":

	https://git.postgresql.org/pg/commitdiff/b284262e40424daa1c546ad76f365b31304d7944

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +