title: Spark specify multiple column conditions for dataframe join
body: <p>How to give more column conditions when joining two dataframes. For example I want to run the following :</p>
  
  <pre><code>val Lead_all = Leads.join(Utm_Master,  
      Leaddetails.columns("LeadSource","Utm_Source","Utm_Medium","Utm_Campaign") ==
      Utm_Master.columns("LeadSource","Utm_Source","Utm_Medium","Utm_Campaign"),
  "left")
  </code></pre>
  
  <p>I want to join only when these columns match. But above syntax is not valid as cols only takes one string. So how do I get what I want.</p>