title: NOT EXISTS on empty table returning false
body: <p>I have a SELECT query across 2 tables that isn't returning any results and I have no idea why it isn't. This is the query that doesn't return any rows:</p>
  
  <pre><code>SELECT b.name, b.description, b.badge_id 
  FROM badges AS b 
  WHERE b.type = 'have' AND b.brand_id = 'zTR7wH5FMl' AND ISNULL(b.series_id) AND b.amount &lt;= 89 
  AND NOT EXISTS (SELECT date_earned 
                  FROM users_badges AS ub 
                  WHERE ub.user_id = 'fMcBBx' AND ub.badge_id = b.badge_id)
  </code></pre>
  
  <p>If I just take off the AND NOT EXISTS clause at the end to check that they haven't already earned the badge I get these results back:</p>
  
  <pre><code>name            description                                             badge_id
  Baker's Dozen   Add 13 items to your Johnny Cupcakes shelf.             sdfKHJkun7
  Cupcaker        Have 82 items on your Johnny Cupcakes shelf.            4MeoheBdik
  Freshly Baked   Have your first item on your Johnny Cupcakes shelf...   kdJGH98NdI
  </code></pre>
  
  <p>Which is exactly what I expect to get. The AND NOT EXISTS check is the only difference. There is no data in the users_badges table yet, so I don't see why it would be returning false. It seems to me that it would be incapable of returning false. Why would it be invalidating the entire query?</p>