MySQL 5.6 Reference Manual Including MySQL NDB Cluster 7.3-7.4 Reference Guide
The DROP FUNCTION statement is used
to drop stored functions and user-defined functions (UDFs):
For information about dropping stored functions, see Section 13.1.26, “DROP PROCEDURE and DROP FUNCTION Statements”.
For information about dropping user-defined functions, see Section 13.7.3.2, “DROP FUNCTION Statement for User-Defined Functions”.