MySQL 5.7 Release Notes
DROP FUNCTION [IF EXISTS] function_name
This statement drops the loadable function named
function_name. (DROP
FUNCTION is also used to drop stored functions; see
Section 13.1.27, “DROP PROCEDURE and DROP FUNCTION Statements”.)
DROP
FUNCTION is the complement of
CREATE
FUNCTION. It requires the
DELETE privilege for the
mysql system database because it removes the
row from the mysql.func system table that
registers the function.
During the normal startup sequence, the server loads functions
registered in the mysql.func table. Because
DROP
FUNCTION removes the mysql.func row
for the dropped function, the server does not load the function
during subsequent restarts.
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.