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.