CREATE FUNCTION Syntax for User-Defined Functions
A user-defined function (UDF) is a way to extend MariaDB with a new function that works like a native (built-in) MariaDB function such as ABS() or CONCAT().
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.
shared_library_name is the basename of the shared object file that contains 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 , "Compiling and Installing User-Defined Functions".
To create a function, you must have the INSERT privilege for the MariaDB database. This is necessary because CREATE FUNCTION adds a row to the mysql.func system table that records the function's name, type, and shared library name. If you do not have this table, you should run the mysql_upgrade command to create it. See , "mysql_upgrade - Check Tables for MariaDB Upgrade".
An active function is one that has been loaded with CREATE FUNCTION and not removed with DROP FUNCTION. 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.
For instructions on writing user-defined functions, see , "Adding a New User-Defined Function". For the UDF mechanism to work, functions must be written in C or C++ (or another language that can use C calling conventions), your operating system must support dynamic loading and you must have compiled mysqld dynamically (not statically).
An AGGREGATE function works exactly like a native MariaDB aggregate (summary) function such as SUM or COUNT(). For AGGREGATE to work, your mysql.func table must contain a type column. If your mysql.func table does not have this column, you should run the mysql-upgrade program to create it (see , "mysql_upgrade - Check Tables for MariaDB Upgrade").Note
To upgrade the shared library associated with a UDF, 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 crash.