title: Ignoring case in spark while joining
body: <p>I have a spark dataframe(<strong>input_dataframe_1</strong>), data in this dataframe looks like as below:</p>
  <pre><code>id              value
   1                Ab
   2                Ai
   3                aB
  </code></pre>
  <p>I have another spark dataframe(<strong>input_dataframe_2</strong>), data in this dataframe looks like as below:</p>
  <pre><code>name              value
   x                ab
   y                iA
   z                aB
  </code></pre>
  <p>I want to join both dataframe and join condition should be case insensitive, below is the join condition I am using:</p>
  <pre><code>output = input_dataframe_1.join(input_dataframe_2,['value'])
  </code></pre>
  <p>How can I make join condition case insensitive?</p>