title: BY statement in SAS proc compare
body: <p>What is the difference in using the ID statement Vs the BY Statement in proc compare.</p>
  
  <p>I understand the ID statement -- that when added observations are compared according to ID..
  but what exactly BY statement does..</p>
  
  <p>I did read the SAS documentation and searched net I couldt understand , can anybody elaborate on it .</p>