title: Joining Spark dataframes on the key
body: <p>I have constructed two dataframes. How can we join multiple Spark dataframes ?</p>
  
  <p>For Example : </p>
  
  <p><code>PersonDf</code>, <code>ProfileDf</code> with a common column as <code>personId</code> as (key).
      Now how can we have one Dataframe combining <code>PersonDf</code> and <code>ProfileDf</code>?         </p>