DO $$
DECLARE  
   a integer := 10;  
   b integer := 20;  
   c integer;  
BEGIN  
   c := a + b;
    RAISE NOTICE'Value of c: %', c;
END $$;

-----------------
CREATE FUNCTION getpersons() RETURNS SETOF person
   LANGUAGE plpgsql AS
$$DECLARE
   overTheAgeOf int := 15;
BEGIN
    RETURN QUERY
       SELECT *
       FROM person
       WHERE age > overTheAgeOf;
END;$$;

SELECT getpersons();