MySQL 5.7 Release Notes
DROP {PROCEDURE | FUNCTION} [IF EXISTS] sp_name
These statements are used to drop a stored routine (a stored
procedure or function). That is, the specified routine is removed
from the server. (DROP FUNCTION is also used to
drop loadable functions; see
Section 13.7.3.2, “DROP FUNCTION Statement for Loadable Functions”.)
To drop a stored routine, you must have the
ALTER ROUTINE privilege for it. (If
the automatic_sp_privileges system variable is
enabled, that privilege and EXECUTE
are granted automatically to the routine creator when the routine
is created and dropped from the creator when the routine is
dropped. See Section 23.2.2, “Stored Routines and MySQL Privileges”.)
The IF EXISTS clause is a MySQL extension. It
prevents an error from occurring if the procedure or function does
not exist. A warning is produced that can be viewed with
SHOW WARNINGS.
DROP FUNCTION is also used to drop
loadable functions (see Section 13.7.3.2, “DROP FUNCTION Statement for Loadable Functions”).