title: Pyspark : How to create union table for some selected columns from df
body: <p>I have below pyspark dataframe -</p>
  <p><a href="https://i.stack.imgur.com/FP3dc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FP3dc.png" alt="enter image description here" /></a></p>
  <p>I want to convert this to. Basically all 3 id columns stacked to each other</p>
  <p><a href="https://i.stack.imgur.com/uRnII.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/uRnII.png" alt="enter image description here" /></a></p>
  <p>I can do this by creating 3 separate dataframe for each of 3 id columns and then do the union of all. But I am looking for a solution which can achieve this in fewer lines because I have at least 25+ id columns in main file.</p>