Re: Parameter placeholders, $n vs ?

Tom Lane <tgl@sss.pgh.pa.us> writes:

> "David G. Johnston" <david.g.johnston@gmail.com> writes:
>> On Thursday, May 24, 2018, Lele Gaifax <lele@metapensiero.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".

Thank you to both. As said, the tool is built on the PG 10 parser extracted as a
standalone library, that serializes the statement AST as JSON. I assumed it
didn't diverge much from what the core parser accepts.

I will clarify my doubt with libpg_query's author.

bye, lele.
-- 
nickname: Lele Gaifax | Quando vivrò di quello che ho pensato ieri
real: Emanuele Gaifas | comincerò ad aver paura di chi mi copia.
lele@metapensiero.it  |                 -- Fortunato Depero, 1929.