Re: Getting error 42P02, despite query parameter being sent

Thanks for replies! I understand now.

Just to clarify user-side motivation: I'm taught that concatenating
data into SQL query strings is bad practice and should be avoided. I
know how to do it safely in my particular case; but apparently the
author of this client library was taught the same, and so their
query-builder doesn't provide the "raw" quoted-interpolation
substitution (the analogue to sql.Literal from Adrian example). Instead
this query-builder relies on the parameters mechanism.

Hence, this limitation forces me to rewrite my query into raw SQL, with
hand-quoting of parameter and query string concatenation.

> if CREATE VIEW stores the Param as a Param

This makes zero sense to me... I assumed that $1 would get substituted
*at query time*, resulting in effectively VALUES ('md5',
'test-param-value') -- not persisted into the view definition. Which is
yes, the former option, Tom; it is sane because that's what $1 does in
every other query type.

If I stare into the abyss regardless, and consider the latter option,
the one that makes no sense to me... I don't see how could it possibly
ever work.

With substitution at some "later time" (expressly not CREATE VIEW query
time), how could this ever work?

CREATE VIEW foobar_view (alg, hash) AS VALUES ('md5', $1); -- suppose
the Param is persisted into view (?!?)

SELECT * from foobar_view where alg = $1;
— is this a 1- or 2-parameter query?
— what do both $1's refer to exactly?
* there's $1 in select query referring to values in column alg, and
* there's $1 supposedly persisted into VALUES of view definition,
referring to a different column with potentially different type.

This makes no sense to me.

So I'm a bit surprised that the (IMO) straightforward semantics of
substitution-at-query-time is not supported.

Nevertheless, acknowledging the "patches welcome" status quo sentiment.
This is helpful; thanks again.

Max

On сб, лис 16 2024 at 11:51:18 -05:00:00, Tom Lane
<tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Achilleas Mantzios <a(dot)mantzios(at)cloud(dot)gatewaynet(dot)com
> <mailto:a(dot)mantzios(at)cloud(dot)gatewaynet(dot)com>> writes:
>> Στις 16/11/24 12:55, ο/η Max Ulidtko έγραψε:
>>> The issue I'm hitting with it is exemplified by server logs like
>>> this:
>>>
>>> 2024-11-16 10:28:19.928 UTC [46] LOG: execute <unnamed>: CREATE
>>> VIEW
>>> public.foobar (alg, hash) AS VALUES ('md5', $1);
>>> 2024-11-16 10:28:19.928 UTC [46] DETAIL: parameters: $1 =
>>> 'test-param-value'
>>> 2024-11-16 10:28:19.928 UTC [46] ERROR: there is no parameter $1 at
>>> character 57
>
>> At least for SQL level prepared statements the statement has to be
>> one of :
>> |SELECT|, |INSERT|, |UPDATE|, |DELETE|, |MERGE|, or |VALUES|
>> |so CREATE is not valid, and I guess the extended protocol prepared
>> statements aint no different in this regard.
>
> Indeed. To some extent this is an implementation limitation: the
> parameter is received (and printed if you have logging enabled),
> but it's not passed down to utility statements such as CREATE VIEW.
> But the reason nobody's been in a hurry to lift that restriction
> is that doing so would open a large can of semantic worms. In a
> case like CREATE VIEW, exactly what is this statement supposed to
> mean? I assume you were hoping that it would result in replacement
> of the Param by a Const representing the CREATE-time value of the
> parameter, but why is that a sane definition? It's certainly not
> what a Param normally does. On the other hand, if CREATE VIEW
> stores the Param as a Param (which is what I think would happen
> if we just extended the parameter-passing plumbing), that's unlikely
> to lead to a good outcome either. There might not be any $1 available
> when the view is used, and if there is one it's not necessarily of
> the right data type.
>
> So, pending some defensible design for what should happen and a patch
> implementing that, we've just left it at the status quo, which is that
> Params are only available to the DML statements Achilleas mentioned.
>
> regards, tom lane