title: Joining two DataFrames and appending where not exists
body: <p>I have two DataFrames. One is a MasterList, the other is an InsertList</p>
  
  <p>MasterList:</p>
  
  <pre class="lang-none prettyprint-override"><code>+--------+--------+
  |  ttm_id|audit_id|
  +--------+--------+
  |       1|      10|
  |      15|      10|
  +--------+--------+
  </code></pre>
  
  <p>InsertList:</p>
  
  <pre class="lang-none prettyprint-override"><code>+--------+--------+
  |  ttm_id|audit_id|
  +--------+--------+
  |       1|      10|
  |      15|       9|
  +--------+--------+
  </code></pre>
  
  <p>In Scala, how do I join two DataFrames but only append to the new DataFrame records</p>
  
  <pre class="lang-sql prettyprint-override"><code>WHERE MasterList.ttm_id = InsertList.ttm_id AND
        MasterList.audit_id != InsertList.audit_id
  </code></pre>
  
  <p>-</p>
  
  <p>ExpectedOutput:</p>
  
  <pre><code>+--------+--------+
  |  ttm_id|audit_id|
  +--------+--------+
  |       1|      10|
  |      15|      10|
  |      15|       9|
  +--------+--------+
  </code></pre>