MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
The DROP FUNCTION statement is used
to drop stored functions and loadable functions:
For information about dropping stored functions, see Section 13.1.27, “DROP PROCEDURE and DROP FUNCTION Statements”.
For information about dropping loadable functions, see Section 13.7.3.2, “DROP FUNCTION Statement for Loadable Functions”.