Lets you store the missing value for a field with the STORE
    statement or the MODIFY statement. When a field is referred to
    as missing, you can think of the field as empty, a field in which
    no value is stored.

    In order to use RDB$MISSING, you must have previously defined
    a missing value for the field when you defined the database.
    If a field is left blank, or you use RDB$MISSING without having
    defined a missing value for that field in its field definition,
    RDML returns an error.

1  –  Format

  (B)0missing-value =

  qqq> RDB$MISSING qqqqqqqqqqqqqqqqq>qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqk
  lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj
  x
  mq>  (  qwq> context-var . field-name qqqqqqqqqqqqqqqwqq>   )  qqq>
           tq> relation-name . field-name qqqqqqqqqqqqqu
           mq> db-handle . relation-name . field-name qj

1.1  –  Format arguments

    context-var            A context variable. A temporary name that
                           you associate with a relation. You define
                           a context variable in a relation clause.
                           For more information see the entry on
                           Context Variables.

    field-name             The name of a field in a relation. For
                           example, once you have defined E as
                           the context variable for the EMPLOYEES
                           relation, E.LAST_NAME is a value
                           expression that refers to a value from
                           the LAST_NAME field of EMPLOYEES.

    relation-name          The name of a relation in the database.

    db-handle              Database handle. A host variable used
                           to refer to a specific database you have
                           invoked. For more information see the
                           entry on the Database Handle clause.

2  –  Examples

    The following programs demonstrate the use of the RDB$MISSING
    value expression with the STORE clause. The programs store the
    specified values for the fields in the DEGREES relation. In these
    programs, a value for DEGREE_FIELD is not specified; instead, the
    RDB$MISSING value expression is specified. This does not actually
    assign a value to the degree field; RDML marks the DEGREE_FIELD
    as empty and stores nothing in this field.

    Note that the C program uses the pad_string function to read
    in the values for the STORE statement. This function pads the
    values stored in each field with the correct number of trailing
    blanks to ensure that the length of the values stored match the
    text size of the field. For more information on pad_string, see
    Appendix B of the "RDML Reference Manual".

2.1  –  C Example

    #include <stdio.h>
    DATABASE PERS = FILENAME "PERSONNEL";

    extern void pad_string();

    main()
    {
    READY PERS;
    START_TRANSACTION READ_WRITE;

    STORE D IN DEGREES USING
       pad_string ("76156", D.EMPLOYEE_ID, sizeof(D.EMPLOYEE_ID));
       pad_string ("HVDU" , D.COLLEGE_CODE, sizeof(D.COLLEGE_CODE));
       D.YEAR_GIVEN = 1978;
       pad_string ("BA", D.DEGREE, sizeof(D.DEGREE));
       pad_string (RDB$MISSING(D.DEGREE_FIELD),D.DEGREE_FIELD,
                   sizeof(D.DEGREE_FIELD));
    END_STORE;

    ROLLBACK;
    FINISH;
    }

2.2  –  Pascal Example

    program store_missing (input,output);
    DATABASE PERS = FILENAME 'PERSONNEL';

    begin
    READY PERS;
    START_TRANSACTION READ_WRITE;

    STORE D IN DEGREES USING
       D.EMPLOYEE_ID := '76156';
       D.COLLEGE_CODE := 'HVDU';
       D.YEAR_GIVEN := 1978;
       D.DEGREE := 'BA';
       D.DEGREE_FIELD := RDB$MISSING(D.DEGREE_FIELD);
    END_STORE;

    ROLLBACK;
    FINISH;
    end.