The DECLARE_VARIABLE clause lets you declare a host language
    variable by referring to a field associated with a database
    relation. The variable inherits the data type and size
    attributes associated with the field. See the BASED ON clause
    for information on declaring program functions: Pascal TYPE(s),
    and C typedef(s).

    The DECLARE_VARIABLE and DEFINE_TYPE clauses have exactly the
    same function. Oracle Rdb decided to rename the clause to clarify
    that its function is to declare host language variables, not to
    define host language types. Note that the DEFINE_TYPE clause
    may still be used; however, Rdb recommends that all new
    applications use the DECLARE_VARIABLE clause in place of the
    DEFINE_TYPE clause.

1  –  Examples

    The following programs demonstrate the use of the
    DECLARE_VARIABLE clause to declare a program variable. These
    programs:

    o  Declare the variable, badge, to have the same data type and
       size attributes as EMPLOYEE_ID in the EMPLOYEES relation.

    o  Use this variable for interactive processing. Note that the
       interactive portion of the programs appear before the READY
       statement. This keeps locks on the database to a minimum.

    o  Select the record from the EMPLOYEES relation that has the
       same value for EMPLOYEE_ID as is stored in badge.

    o  Modify the STATUS_CODE field of this record

    Note that the C program uses the read_string function to prompt
    for and receive a value for badge. For more information on this
    function see Appendix B of the "RDML Reference Manual".

1.1  –  C Example

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

    extern void read_string();
    static DECLARE_VARIABLE badge SAME AS EMPLOYEES.EMPLOYEE_ID;

    main()
    {
    read_string ("Employee ID: ", badge, sizeof(badge));

    READY PERS;
    START_TRANSACTION READ_WRITE;

    FOR E IN EMPLOYEES WITH E.EMPLOYEE_ID = badge
       MODIFY E USING
          strcpy(E.STATUS_CODE,"1");
       END_MODIFY;
    END_FOR;

    ROLLBACK;
    FINISH;
    }

1.2  –  Pascal Example

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

    var
       DECLARE_VARIABLE badge SAME AS EMPLOYEES.EMPLOYEE_ID;

    begin
    write  ('Employee ID: ');
    readln (badge);

    READY PERS;
    START_TRANSACTION READ_WRITE;

    FOR E IN EMPLOYEES WITH E.EMPLOYEE_ID = badge
       MODIFY E USING
          E.STATUS_CODE := '1';
       END_MODIFY;
    END_FOR;

    ROLLBACK;
    FINISH;
    end.

2  –  Format

  (B)0DECLARE_VARIABLE   qqqqqqqqqqqqqqqqqq>  host-variable  qqqk
                                                            x
  lqqqqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqqqj
  mqqwqq>qqqqqqqwqq> AS qqwqq>qqqqqqqqqqqqqqqqqqqwqqk
     mqq> SAME qj         mqq> db-handle qq> . qqj  x
                                                    x
   lqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqj
   mqqqqqqqqqqqq>  relation-name  qqq>  .  qqq> field-name qqq>

2.1  –  Format arguments

    host-variable          A valid host language variable.

    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.

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

    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.