A user-defined function (UDF) is a way to extend MySQL with a new
function that works like native (built in) MySQL function such as
ABS() and CONCAT().

AGGREGATE is a new option for MySQL 3.23.  An
AGGREGATE function works exactly like a native MySQL
GROUP function like SUM or COUNT().

CREATE FUNCTION saves the function's name, type, and shared library
name in the mysql.func system table.  You must have the
INSERT and DELETE privileges for the mysql database
to create and drop functions.
