Drops the definition of the specified function or specific function from the Data Dictionary and from the containing database or user.
You cannot drop an external UDF being used as a cast, ordering, or transform routine. You must first drop the definition for the cast, ordering, or transform. See DROP CAST, DROP ORDERING, or DROP TRANSFORM.
This statement is ANSI SQL:2011 compliant.
You must have the DROP FUNCTION privilege on an external or SQL function or its containing database or user to drop it.
In addition, you must remove the UDF from any constraint objects that reference it before dropping the UDF.