Deletes one or more field definitions. When the DELETE FIELD
    statement executes, Oracle Rdb deletes the field definition from the
    physical database. If you invoke the database using the PATHNAME
    argument, Oracle Rdb also deletes the field definition from the
    CDD$DATABASE definition of the database in the data dictionary.
    You can delete any named field, whether it was defined with a
    DEFINE FIELD statement or with a DEFINE RELATION statement.
    However, you cannot delete a field that is referred to in the
    definition of a relation, index, or constraint:

    Example:

    DELETE FIELD POSTAL_CODE.