Tests for the presence of a single record in a record stream.
    A UNIQUE conditional expression is true if the record stream
    specified by the record selection expression consists of only one
    record.

    If you precede the UNIQUE expression with the optional NOT
    qualifier, the condition is true if there is more than one record
    in the record stream or if the stream is empty.

1  –  Examples

    The following programs demonstrate the use of the UNIQUE
    conditional expression. These programs join the relations
    EMPLOYEES and DEGREES over their common field, EMPLOYEE_ID. The
    UNIQUE expression limits the record stream to those records in
    the EMPLOYEES relation that have only one corresponding record
    in the DEGREES relation. These programs print an informational
    message and the selected employees first and last name in
    alphabetical order, based on the last name.

1.1  –  C Example

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

    main()
    {
    READY PERS;
    START_TRANSACTION READ_ONLY;

    FOR E IN EMPLOYEES
        SORTED BY E.FIRST_NAME
        WITH UNIQUE D IN DEGREES WITH D.EMPLOYEE_ID = E.EMPLOYEE_ID
           printf("%s %s has one and only one college degree.\n",
                         E.FIRST_NAME, E.LAST_NAME);
    END_FOR;

    COMMIT;
    FINISH;
    }

1.2  –  Pascal Example

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

    begin
    READY PERS;
    START_TRANSACTION READ_ONLY;

    FOR E IN EMPLOYEES
       WITH UNIQUE D IN DEGREES WITH D.EMPLOYEE_ID = E.EMPLOYEE_ID
          writeln (E.FIRST_NAME, ' ', E.LAST_NAME,
                  ' has one and only one college degree.');
    END_FOR;

    COMMIT;
    FINISH;
    end.

2  –  Format

  (B)0unique-clause =

    qqqwqq>qqqqqqqwqqqqqqqqqq> UNIQUE qqqqqqwq>qqqqqqqqqqqqqqqqqqwqqqqk
       mqq> NOT qqj                         mq> handle-options qqj    x
                                                                      x
     lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj
     mqqqqqqqqqqqqqq>  rse  qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq>

  (B)0handle-options =

  q> ( qwqqqqqq>  REQUEST_HANDLE  qqqqq>  var qqqqqqqqwq> ) q>
        tqqqqqq> TRANSACTION_HANDLE qqq>  var qqqqqqqqu
        mqqqqqq> REQUEST_HANDLE q> var q> , qqqqqqqk  x
          lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj  x
          mqqqq> TRANSACTION_HANDLE q> var qqqqqqqqqqqj

2.1  –  Format arguments

    rse                    A record selection expression. A phrase
                           that defines specific conditions that
                           individual records must meet before
                           Oracle Rdb includes them in a record stream.

    handle-options         A request handle, a transaction handle, or
                           both.

    REQUEST_HANDLE var     The REQUEST_HANDLE keyword followed by a
                           host language variable. A request handle
                           identifies a compiled Oracle Rdb request.
                           If you do not supply a request handle
                           explicitly, RDML associates a unique
                           request handle for the compiled request.

    TRANSACTION_HANDLE     The TRANSACTION_HANDLE keyword followed by
    var                    a host language variable. A transaction
                           handle identifies a transaction. If
                           you do not supply a transaction handle
                           explicitly, RDML uses the default
                           transaction handle.