Re: proposal: schema variables

čt 27. 2. 2020 v 15:59 odesílatel DUVAL REMI <REMI(dot)DUVAL(at)cheops(dot)fr> napsal:

> Hello Pavel.
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> That looks pretty good to me !
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> I’m adding Philippe Beaudoin who was also interested in this topic.
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> Recap : We were looking for a way to separate variable from constants in
> the “Schema Variables” proposition from Pavel.
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> Pavel was saying that there are some limitations regarding the keywords we
> can use, as the community don’t want to introduce too much new keywords in
> Postgres SQL (PL/pgSQL is a different list of keywords).
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> “CONSTANT” is not a keyword in SQL for Now (though it is one in PL/pgSQL).
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> Pavel’s syntax allow to use it as a keyword in the “WITH OPTIONS” clause
> that is already supported.
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> … I think it’s a good idea.
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> The list of keywords is defined in : postgresql\src\include\parser\kwlist.h
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> Pavel, I saw that in DB2, those variables are called “Global Variables”,
> is it something we can consider changing, or do you prefer to keep using
> the “Schema Variable” name ?
>

It is most hard question. Global variables has sense, but when we will use
it in plpgsql, then this name can be little bit confusing. Personally I
prefer "schema variable" although my opinion is not too strong. This name
more signalize so this is more generic, more database related than some
special kind of plpgsql variables. Now, I think so maybe is better to use
schema variables, because there is different syntax then global temp
tables. Variables are global by design. So in this moment I prefer the name
"schema variables". It can be used as global variables in plpgsql, but it
is one case.

Pavel

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> *De :* Pavel Stehule [mailto:pavel(dot)stehule(at)gmail(dot)com]
> *Envoyé :* jeudi 27 février 2020 15:38
> *À :* DUVAL REMI <REMI(dot)DUVAL(at)CHEOPS(dot)FR>
> *Cc :* PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
> *Objet :* Re: proposal: schema variables
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> Hi
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> 3) Any way to define CONSTANTs ?
> We already talked a bit about this subject and also Gilles Darold
> introduces it in this mailing-list topic but I'd like to insist on it.
> I think it would be nice to have a way to say that a variable should not
> be changed once defined.
> Maybe it's hard to implement and can be implemented later, but I just want
> to know if this concern is open.
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> I played little bit with it and I didn't find any nice solution, but maybe
> I found the solution. I had ideas about some variants, but almost all time
> I had a problem with parser's shifts because all potential keywords are not
> reserved.
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> last variant, but maybe best is using keyword WITH
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> So the syntax can looks like
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> CREATE [ TEMP ] VARIABLE varname [ AS ] type [ NOT NULL ] [ DEFAULT
> expression ] [ WITH [ OPTIONS ] '(' ... ')' ] ]
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> What do you think about this syntax? It doesn't need any new keyword, and
> it easy to enhance it.
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> CREATE VARIABLE foo AS int DEFAULT 10 WITH OPTIONS ( CONSTANT);
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> ?
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> Regards
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> Pavel
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