Great! Now that you've got a basic grasp on functions, let's briefly review what have we learned in this part:

• User-defined functions extend the functionality of a database.
• The primary advantages of using user-defined functions are code re-usability and custom logic.
• We use the CREATE FUNCTION statement to create a new function:

  CREATE FUNCTION get_circumference(diameter decimal)
  RETURNS decimal AS $$
  BEGIN
    RETURN get_pi() * diameter;
  END;
  $$ LANGUAGE PLpgSQL;
  

• Warning: each database engine (Oracle, SQL Server, etc.) has slightly different syntax for creating functions, though the concepts are similar in all database engines.
• PL/pgSQL is the most common language for writing a function in PostgreSQL. You can use other languages (like Perl, Python, etc.), but they are less frequently used.