7.33 CREATE FUNCTION/DROP FUNCTION syntax

CREATE [AGGREGATE] FUNCTION function_name RETURNS {STRING|REAL|INTEGER}
       SONAME shared_library_name

DROP FUNCTION function_name

A user-definable function (UDF) is a way to extend MySQL with a new function that works like native (built in) MySQL functions 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.

All active functions are reloaded each time the server starts, unless you start mysqld with the --skip-grant-tables option. In this case, UDF initialization is skipped and UDFs are unavailable. (An active function is one that has been loaded with CREATE FUNCTION and not removed with DROP FUNCTION.)

For instructions on writing user-definable functions, see section 16 Adding new functions to MySQL. For the UDF mechanism to work, functions must be written in C or C++, your operating system must support dynamic loading and you must have compiled mysqld dynamically (not statically).