Re: proposal: schema variables - Mailing list pgsql-hackers

čt 27. 2. 2020 v 15:37 odesílatel Pavel Stehule <pavel.stehule@gmail.com> napsal:

Hi

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.

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.

last variant, but maybe best is using keyword WITH

So the syntax can looks like

CREATE [ TEMP ] VARIABLE varname [ AS ] type [ NOT NULL ] [ DEFAULT expression ] [ WITH [ OPTIONS ] '(' ... ')' ] ]

What do you think about this syntax? It doesn't need any new keyword, and it easy to enhance it.

CREATE VARIABLE foo AS int DEFAULT 10 WITH OPTIONS ( CONSTANT);

After some more thinking and because in other patch I support syntax CREATE TRANSACTION VARIABLE ... I change my opinion and implemented support for 

syntax CREATE IMMUTABLE VARIABLE for define constants.

See attached patch

Regards

Pavel

 

?

Regards

Pavel