title: SELECT COUNT(DISTINCT... ) error on multiple columns?
body: <p>I have a table, VehicleModelYear, containing columns id, year, make, and model.</p>
  
  <p>The following two queries work as expected:</p>
  
  <pre><code>SELECT DISTINCT make, model
  FROM VehicleModelYear
  
  SELECT COUNT(DISTINCT make)
  FROM VehicleModelYear
  </code></pre>
  
  <p>However, this query doesn't work</p>
  
  <pre><code>SELECT COUNT(DISTINCT make, model)
  FROM VehicleModelYear
  </code></pre>
  
  <p>It's clear the answer is the number of results returned by the first query, but just wondering what is wrong with this syntax or why it doesn't work.</p>