CREATE FUNCTION UDF

Install a user-defined function from a shared library. This command loads an external compiled function into the server for extended capabilities.

Syntax

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

Description

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.

To create a function, you must have the INSERT privilege for the mysql database. This is necessary becauseCREATE 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 mariadb-upgrade command to create it.

UDFs need to be written in C, C++ or another language that uses C calling conventions, MariaDB needs to have been dynamically compiled, and your operating system must support dynamic loading.

For an example, see sql/udf_example.cc in the source tree. For a collection of existing UDFs see sql-udf.

Statements making use of user-defined functions are not safe for replication.

For creating a stored function as opposed to a user-defined function, see CREATE FUNCTION.

For valid identifiers to use as function names, see Identifier Names.

RETURNS

The RETURNS clause indicates the type of the function's return value, and can be one of string, INTEGER, REAL or DECIMAL. DECIMAL functions currently return string values and should be written like STRING functions.

shared_library_name

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. Note that before MariaDB/MySQL 5.1, the shared object could be located in any directory that was searched by your system's dynamic linker.

AGGREGATE

Aggregate functions are summary functions such as SUM() and AVG(). Aggregate UDF functions can be used as window functions.

OR REPLACE

If the optional OR REPLACE clause is used, it acts as a shortcut for:

DROP FUNCTION IF EXISTS function_name;
CREATE FUNCTION name ...;

IF NOT EXISTS

When the IF NOT EXISTS clause is used, MariaDB will return a warning instead of an error if the specified function already exists. Cannot be used together with OR REPLACE.

Upgrading a UDF

To upgrade the UDF's shared library, first run a DROP FUNCTION statement, then upgrade the shared library and finally run the CREATE FUNCTION statement. If you upgrade without following this process, you may crash the server.

Examples

CREATE FUNCTION jsoncontains_path RETURNS INTEGER SONAME 'ha_connect.so';
Query OK, 0 rows affected (0.00 sec)

OR REPLACE and IF NOT EXISTS:

CREATE FUNCTION jsoncontains_path RETURNS INTEGER SONAME 'ha_connect.so';
ERROR 1125 (HY000): Function 'jsoncontains_path' already exists

CREATE OR REPLACE FUNCTION jsoncontains_path RETURNS INTEGER SONAME 'ha_connect.so';
Query OK, 0 rows affected (0.00 sec)

CREATE FUNCTION IF NOT EXISTS jsoncontains_path RETURNS INTEGER SONAME 'ha_connect.so';
Query OK, 0 rows affected, 1 warning (0.00 sec)

SHOW WARNINGS;
+-------+------+---------------------------------------------+
| Level | Code | Message                                     |
+-------+------+---------------------------------------------+
| Note  | 1125 | Function 'jsoncontains_path' already exists |
+-------+------+---------------------------------------------+

See Also

• Identifier Names

• DROP FUNCTION

• CREATE FUNCTION

_{This page is licensed: GPLv2, originally from fill_help_tables.sql}