title: HASHBYTES() function
body: <p>How to use HASHBYTES() in TSQL code?</p>
  
  <p>the problem with my code is </p>
  
  <pre><code>UPDATE mytable 
     SET hash_value=HASHBYTES('MD5',convert(varchar(max),col1),convert(varchar(max),col2),..)
  </code></pre>
  
  <p>returns <code>NULL</code>.
  Can you advise me, what's wrong with my code?</p>