title: Difference between SET SCAN & SET DEFINE
body: <p>Why do in SQL*PLUS we have SET SCAN and SET DEFINE both ?
  I know both are used interchangeably in SQL.
  I tested and found that if i set any of them OFF, substitution variables will not work.
  Is their any specific case where we need both and importance of both can be understood simultaneously?</p>
  
  <p>Thanks in advance.</p>