title: How to display message instead of NULL
body: <p>I am returning a query with names, courses and course codes, but where the course code is null i would like to display "NOT ENROLLED".
  Could I do this by using a 'default'?
  The select statement is coming from a VIEW would this make any difference.</p>
  
  <pre><code>CREATE VIEW STUDENT_LIST
  (studentname, dateofbirth, coursecode)
  AS 
  SELECT COURSECODE, STUDENTNAME, DATEOFBIRTH
  FROM STUDENT;
  
  SELECT STUDENTNAME, DATEOFBIRTH, NVL(COURSECODE,"NOT_ENROLLED")
  FROM STUDENT_LIST;
  </code></pre>
  
  <p>I get the reply NOT ENROLLED invalid identifier... I have tried without quotes 
  I am using oracle.</p>