title: TSQL Count 'Where' Condition
body: <p>How do I implement the 'meaning' of the following psuedo-SQL statement:</p>
  
  <pre><code>COUNT(distinct id where attribute1 &gt; 0)
  </code></pre>
  
  <p>In other words, how do I make conditional, distinct counting statements?</p>
  
  <p>Thanks!</p>