Re: [HACKERS] proposal: session server side variables - Mailing list pgsql-hackers

Hello Pavel, and Happy new year!

(1) Having some kind of variable, especially in interactive mode, allows to

manipulate previous results and reuse them later, without having to
resort to repeated sub-queries or to retype non trivial values.

Client side psql :-variables are untyped and unescaped, thus not very
convenient for this purpose.

You can currently (ab)use user defined GUCs for this.

How? It seems that I have missed the syntax to assign the result of a
query to a user-defined guc, and to reuse it simply in a query.

postgres=# select set_config('myvar.text', (select
current_timestamp::text), false);

Thanks for the pointer! The documentation is rather scarse...

They are indeed session or transaction-alive. They seem to be user-private, which is good. However they are text only, casts are needed in practice as shown by your example, and I find the syntax quite unfriendly for interactive use. I'm not sure about performance.

I have added a subsection about them in the wiki.

--
Fabien.