Oracle PL/SQL allows the use of package variables. PL/SQL is +/- ADA language - and package variables are "global" variables. They are not directly visible from SQL, but Oracle allows reduced syntax for functions without arguments, so you need to write a wrapper
CREATE OR REPLACE PACKAGE my_package AS FUNCTION get_a RETURN NUMBER; END my_package; /
CREATE OR REPLACE PACKAGE BODY my_package AS a NUMBER(20);
FUNCTION get_a RETURN NUMBER IS BEGIN RETURN a; END get_a; END my_package;
SELECT my_package.get_a FROM DUAL;
Inside SQL the higher priority has SQL, inside non SQL commands like CALL or some PL/SQL command, the higher priority has packages.
The risk of collision's identifier is in some PL/SQL statements less than in Postgres, because SQL can be used only on dedicated positions (minimally in older Oracle's versions). Against other databases there is not allowed to use SQL everywhere as an expression. PL/SQL is an independent language, environment with its own expression executor (compiler). Other databases allow you to use an SQL subselect (I tested MySQL, PL/pgSQL, and I think (if I remember docs well) it is in standard SQL/PSM (related part of ANSI/SQL)) as expression. The integration of SQL into PL/SQL is not too deep and stored procedures look more like client code executed on the server side.
