Emulate procedural languages in H2

[lukaseder]

Procedural languages can be emulated in H2 using Java code. For example, this PostgreSQL program:

DO $$
BEGIN
  FOR i IN 1 .. 10 LOOP
    RAISE INFO '%', i;
  END LOOP;
END;
$$

... can be written as follows in H2

CREATE ALIAS x AS $$
void x() {
  for (int i = 1; i <= 10; i++)
    System.out.println(i);
}
$$;

CALL x();

DROP ALIAS x;

A future version might even support a DO syntax, akin to PostgreSQL: h2database/h2database#1723

DO $$
void x() {
  for (int i = 1; i <= 10; i++)
    System.out.println(i);
}
$$;

[lukaseder]

This first implementation is clearly experimental. The following follow up issues need to be addressed:

• Add a flag to generate Java code from various expressions #8303 Add a flag to generate Java code from various expressions
• Emulate procedural languages in H2 for Java 6 #8304 Emulate procedural languages in H2 for Java 6
• Emulate hiding local variables where not supported #8307 Variable block scope emulation