title: Pyspark - how to do case insensitive dataframe joins?
body: <p>Is there any nice looking code to perform case insensitive join in Pyspark?
  Something like:</p>
  
  <pre class="lang-py prettyprint-override"><code>df3 = df1.join(df2, 
                 ["col1", "col2", "col3"],
                 "left_outer",
                 "case-insensitive")
  </code></pre>
  
  <p>Or what is your working solutions to this?</p>