DROP FUNCTION udf_name
DROP FUNCTION
statement uninstalls a user-defined function UDF with the specified name. Upon successful removal, the function will no longer be available for use in subsequent queries. However, ongoing concurrent queries will not be affected, and if necessary, the library unloading will be delayed until those queries are completed. Example:
mysql> DROP FUNCTION avgmva;
Query OK, 0 rows affected (0.00 sec)