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.
You cannot drop a UDF that is referenced in a row-level security constraint definition if the constraint is assigned to a user, profile, or table. You can use ALTER CONSTRAINT to drop or replace a UDF from a row-level security constraint definition, and then drop the UDF. See ALTER CONSTRAINT.
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.