title: Exclude null results on a UNION query
body: <p>I have the following query, which gives me the provider for a given title:</p>
  
  <pre><code>SELECT DISTINCT(provider) FROM 
      (SELECT title, provider FROM financials_raw 
          UNION 
          SELECT title, provider from sales_raw
      ) combined 
          WHERE title = 'Home'
  </code></pre>
  
  <p>However, this will return NULL provider results as well, how would I exclude all null results?</p>