title: impala split_part function not accepting negative indexing
body: <p>I'm trying to access the second to last element in a split_part function. as I saw you should be able to use a negative index to look right to left.
  In impala however is get a &quot;invalid field position&quot; error</p>
  <pre><code>SELECT split_part(string1;string2;string3;string4, &quot;;&quot;, -2)
  </code></pre>
  <pre><code>SELECT split_part(string3;string4, &quot;;&quot;, -2)
  </code></pre>
  <pre><code>SELECT split_part(string2;string3;string4, &quot;;&quot;, -2)
  </code></pre>
  <p>I was hoping to get &quot;string3&quot; returned for all the above examples.
  Any help on how to do this in Impala would be much appreciated</p>