title: SQL Pivot IF EXISTS
body: <p>I think I need a PIVOT but I'm yet to find an example that uses only 1 column.<br />
  Current data</p>
  
  <pre><code>CustID       Value                
  1              A                   
  1              B
  1              C                  
  2              A                   
  3              B                  
  4              A
  4              C  
  </code></pre>
  
  <p>I need</p>
  
  <pre><code>StudentNumber      A      B     C
  1                  Yes   Yes  Yes
  2                  Yes   No    No
  3                  No    Yes   No
  4                  Yes   No    Yes
  </code></pre>
  
  <p>I appreciate it's probably a very simple query but I really am struggling!</p>