Changes the definition of the fields and relation-specific
    constraints that make up a relation. You can add, delete, or
    change fields and relation-specific constraints in an existing
    relation. When you execute this statement, Oracle Rdb modifies the
    named field and relation-specific constraint definition(s) within
    the relation definition. All the fields that you do not mention
    remain the same.

    Example:

    RDO> CHANGE RELATION EMPLOYEES.
    cont>     DEFINE SALARY.
    cont> END EMPLOYEES RELATION.
    RDO> !
    RDO> CHANGE RELATION DEPARTMENTS.
    cont>    CHANGE DEPARTMENT_NAME
    cont>        QUERY_NAME FOR DATATRIEVE IS "DEPT".
    cont> END DEPARTMENTS RELATION.