(B)0cross-clause =

  qwq> CROSS qq> relation-clause qwqqqqqqqqqqqqqqqqqqqqqqqqqqqqwqwqq>
   x                              mqq> OVER qwq> field-name qwqj x
   x                                         mqqqqqq , <qqqqqj   x
   mqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj

    Lets you combine records from two or more record streams. You
    can join these records in combinations based on the relationship
    between the values of fields in the separate record streams. This
    combining of records is called a relational join.

1  –  More

    The RDO documentation indicates that views do not allow
    updates to returned data. They do not specify this
    restriction on a cross of two relations from the same
    database. Oracle Rdb allows it to work if you use a WITH
    clause.

    Any field that appears in the RSE (record selection
    expression) is marked as read-only. You cannot update these
    fields as this may remove the record from the join, or add
    a new record to the join that will not be recognized.

    In general, the record stream created by a join (CROSS)
    cannot be updated. A workaround is to fetch the RDB$DB_KEY
    in the loop and generate a separate FOR loop to modify the
    value. The following example shows this situation:

    #include stdio

    DATABASE MAPB = FILENAME "[rdml]PERSONNEL";

    main()
    {
     READY MAPB;
     START_TRANSACTION READ_WRITE;

     printf("Entering EMPLOYEES & JOB_HISTORY relations:\n\n");

     FOR E IN EMPLOYEES
        CROSS JH IN JOB_HISTORY OVER EMPLOYEE_ID
        WITH (JH.EMPLOYEE_ID > "00000" OR E.FIRST_NAME STARTING
        WITH "A-")
        SORTED BY E.LAST_NAME

        FOR E1 IN EMPLOYEES WITH E1.RDB$DB_KEY = E.RDB$DB_KEY
        printf("\n\n%s %s < found  ",E1.FIRST_NAME ,E1.LAST_NAME);

        MODIFY E1 USING
        strcpy(E1.FIRST_NAME,"Xavier    ");

        printf("\n%s %s < changed",E1.FIRST_NAME,E.LAST_NAME);
        END_MODIFY;
        END_FOR;

     END_FOR;

     printf("\n\nRolling Back the modifys");
     ROLLBACK;

     FINISH;
     printf("\n\nFinished");
    }