title: pyspark merge/join two data frame
body: <p>I want to merge two data frame.</p>
  
  <p>list 1:</p>
  
  <pre><code>      id        
  0   1234
  1   456
  2   789
  3   101112
  </code></pre>
  
  <p>list 2: </p>
  
  <pre><code>      id    age        
  0   456      18
  1   101112   52
  </code></pre>
  
  <p>Desired result:</p>
  
  <pre><code>      id    age     
  0   1234     Na
  1   456      18
  2   789      Na
  3   101112   52
  </code></pre>
  
  <p>tried:</p>
  
  <pre><code>list1.join(list2,list1.id==list2.id,'inner')
  </code></pre>
  
  <p>error:</p>
  
  <pre><code>ValueError: Can only compare identically-labeled Series objects
  </code></pre>
  
  <p>tried:</p>
  
  <pre><code>list1.merge(list2)
  </code></pre>
  
  <p>error:</p>
  
  <p>result is list 2.</p>
  
  <p>what is the problem?</p>