title: md5 in bigquery
body: <p>In BigQuery, I'm using md5 function as: </p>
  
  <pre><code>select md5('&lt;&lt;some string&gt;&gt;') as hashed
  </code></pre>
  
  <p>which always returns "==" in the last of the letter like: </p>
  
  <pre><code>R7zlx09Yn0hn29V+nKn4CA==    
  </code></pre>
  
  <p>Why does '==' always come with it? </p>