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CREATE FUNCTION/DROP FUNCTION
Syntax
CREATE [AGGREGATE] FUNCTION function_name RETURNS {STRING|REAL|INTEGER} SONAME shared_library_name DROP FUNCTION function_name |
ABS()
and CONCAT()
.
AGGREGATE
is a new option for MySQL Version 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-defined functions, see 21.2 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).
Note that to make AGGREGATE
work, you must have a
mysql.func
table that contains the column type
. If you do not
have this table, you should run the script
mysql_fix_privilege_tables
to create it.