15.7.4.1 CREATE FUNCTION Statement for Loadable Functions

CREATE [AGGREGATE] FUNCTION [IF NOT EXISTS] function_name
    RETURNS {STRING|INTEGER|REAL|DECIMAL}
    SONAME shared_library_name

This statement loads the loadable function named function_name. (CREATE FUNCTION is also used to created stored functions; see Section 15.1.17, “CREATE PROCEDURE and CREATE FUNCTION Statements”.)

A loadable function is a way to extend MySQL with a new function that works like a native (built-in) MySQL function such as ABS() or CONCAT(). See Adding a Loadable Function.

function_name is the name that should be used in SQL statements to invoke the function. The RETURNS clause indicates the type of the function's return value. DECIMAL is a legal value after RETURNS, but currently DECIMAL functions return string values and should be written like STRING functions.

IF NOT EXISTS prevents an error from occurring if there already exists a loadable function with the same name. It does not prevent an error from occurring if there already exists a built-in function having the same name. IF NOT EXISTS is also supported for CREATE FUNCTION statements. See Function Name Resolution.

The AGGREGATE keyword, if given, signifies that the function is an aggregate (group) function. An aggregate function works exactly like a native MySQL aggregate function such as SUM() or COUNT().

shared_library_name is the base name of the shared library file containing the code that implements the function. The file must be located in the plugin directory. This directory is given by the value of the plugin_dir system variable. For more information, see Section 7.7.1, “Installing and Uninstalling Loadable Functions”.

CREATE FUNCTION requires the INSERT privilege for the mysql system schema because it adds a row to the mysql.func system table to register the function.

CREATE FUNCTION also adds the function to the Performance Schema user_defined_functions table that provides runtime information about installed loadable functions. See Section 29.12.22.11, “The user_defined_functions Table”.

Note

Like the mysql.func system table, the Performance Schema user_defined_functions table lists loadable functions installed using CREATE FUNCTION. Unlike the mysql.func table, the user_defined_functions table also lists loadable functions installed automatically by server components or plugins. This difference makes user_defined_functions preferable to mysql.func for checking which loadable functions are installed.

During the normal startup sequence, the server loads functions registered in the mysql.func table. If the server is started with the --skip-grant-tables option, functions registered in the table are not loaded and are unavailable.

Note

To upgrade the shared library associated with a loadable function, issue a DROP FUNCTION statement, upgrade the shared library, and then issue a CREATE FUNCTION statement. If you upgrade the shared library first and then use DROP FUNCTION, the server may unexpectedly shut down.