The DECODE function compares an expression to each supplied
    search value until a match is found. When a match is found,
    DECODE returns the result in the corresponding result field. If
    no match is found, DECODE returns the default if it is specified,
    null if no default is specified.

    Example: Using the DECODE function

    SQL> SELECT employee_id, last_name, first_name,
    cont> DECODE (status_code, '1', 'Full time',
    cont>                      '2', 'Part time')
    cont> FROM employees
    cont> LIMIT TO 5 ROWS;
     EMPLOYEE_ID   LAST_NAME       FIRST_NAME
     00165         Smith           Terry        Part time
     00190         O'Sullivan      Rick         Full time
     00187         Lasch           Stan         Full time
     00169         Gray            Susan        Full time
     00176         Hastings        Norman       Full time
    5 rows selected