PL/pgSQL Function

How to write an overloaded set of hello_world functions in PostgreSQL PL/pgSQL. The following code lets you write and test overloaded functions and the concepts of null, zero-length string, and string values.

-- Drop the overloaded functions.
DROP FUNCTION IF EXISTS hello_world(), hello_world(whom VARCHAR);

-- Create the function.
CREATE FUNCTION hello_world()
RETURNS text AS
$$
DECLARE
  output  VARCHAR(20);
BEGIN
  /* Query the string into a local variable. */
  SELECT 'Hello World!' INTO output;
 
  /* Return the output text variable. */
  RETURN output;
END
$$ LANGUAGE plpgsql;

-- Create the function.
CREATE FUNCTION hello_world(whom VARCHAR)
RETURNS text AS
$$
DECLARE
  output  VARCHAR(20);
BEGIN
  /* Query the string into a local variable. */
  IF whom IS NULL OR LENGTH(whom) = 0 THEN
    SELECT 'Hello World!' INTO output;
  ELSE
    SELECT CONCAT('Hello ', whom, '!') INTO output;
  END IF;

 
  /* Return the output text variable. */
  RETURN output;
END
$$ LANGUAGE plpgsql;

-- Call the function.
SELECT hello_world();
SELECT hello_world(Null) AS output;
SELECT hello_world('') AS output;
SELECT hello_world('Harry') AS output;

It should print:

    output
--------------
 Hello World!
(1 row)

    output
--------------
 Hello World!
(1 row)

    output
--------------
 Hello World!
(1 row)

    output
--------------
 Hello Harry!
(1 row)

As always, I hope this helps those looking for the basics and how to solve problems.