Re: Parameter placeholders, $n vs ?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>
Cc: Lele Gaifax <lele(at)metapensiero(dot)it>, "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org>
Subject: Re: Parameter placeholders, $n vs ?
Date: 2018-05-24 14:02:57
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"David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> On Thursday, May 24, 2018, Lele Gaifax <lele(at)metapensiero(dot)it> wrote:
>> So the questions: is the '?' style placeholder a supported variant? and
>> if so, should the ParamRef doc tell something about that?

> PostgreSQL's Prepare statement doesn't accept question mark as a parameter
> symbol, and cannot ever because it is already a valid operator symbol.

To enlarge on that a bit:

* PG's core parser certainly does not accept ? as a parameter symbol.
I speculate that you fed the input through some frontend that converts
? to $n (JDBC, perhaps)?

* The only thing in the core code that would print a ParamRef in any
sort of symbolic form is _outParamRef, and it's easily seen by inspection
to be incapable of omitting the "number" field ... not to mention that
it doesn't emit the JSON-esque representation you're showing us. So
that behavior must also be due to some non-core pretty-printing code you
haven't identified to us. No idea what rules that might have for deciding
to omit "number".

regards, tom lane

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