Structure of a PL/pgSQL function

It doesn't take much to get a PL/pgSQL function working. Here is a very basic example:

CREATE FUNCTION mid(varchar, integer, integer) RETURNS varchar
AS $$
BEGIN
  RETURN substring($1,$2,$3);
END;
$$
LANGUAGE plpgsql;

The previous function shows the minimal elements of a PL/pgSQL function. It creates an alias for the substring built-in function called mid. This is a handy alias to have around for developers that come from Microsoft SQL Server or MySQL and are wondering what happened to the mid function. It also illustrates the most basic parameter passing strategy. The parameters are not named and are accessed in the function by relative location from left to right.

The basic elements are name, parameters, return type, body, and language. It could be argued that parameters are not mandatory for a function and neither is the return value. This might be useful for a procedure that operates on data without providing a response, but it would be prudent to return...