title: How to select all columns of a dataframe in join - Spark-scala
body: <p>I am doing join of 2 data frames and select all columns of left frame for example:</p>
  
  <pre><code>val join_df = first_df.join(second_df, first_df("id") === second_df("id") , "left_outer")
  </code></pre>
  
  <p>in above I want to do select first_df.* .How can I select all columns of one frame in join ?</p>