title: Efficient Join in hive without OR condition
body: <p>I need to join geographical region table to user's table in <code>Hive</code>.
  geographical region can be country, state or city level. 
  When geographical region is county level, I need to select all the listings in that county so on. My version of hive does not allow OR in join condition.</p>
  
  <p>What is the most efficient way to write this query?</p>
  
  <p>For example,</p>
  
  <p>Region table</p>
  
  <pre><code>region_id , city, state, country
  1,  Rome, NULL , IT
  2, NULL, NULL, BM
  3, VANCOUVER, BC, CA
  </code></pre>
  
  <p>User table</p>
  
  <pre><code>user_id, city , state, country
  103 , VANCOUVER , BC , CA
  105 , HAMILTON, NULL, BM
  106 , NULL, NULL, BM
  </code></pre>
  
  <p>Result table</p>
  
  <pre><code>region_id, user_id, city, state, country
  3, 103 , VANCOUVER , BC , CA
  2, 105 , HAMILTON, NULL, BM
  2, 106 , NULL, NULL, BM
  </code></pre>