title: Remove subsequent duplicate string in a column of table
body: <p>I have a table named <code>event</code></p>
  
  <pre><code>id     event_sequnce
  1      a-&gt;c-&gt;b-&gt;b-&gt;b-&gt;c-&gt;b
  2      d-&gt;d-&gt;a-&gt;d-&gt;c-&gt;a-&gt;a-&gt;c
  </code></pre>
  
  <p>I want to remove the subsequent duplicate letter from the column <code>event_sequnce</code></p>
  
  <p>so output table will be</p>
  
  <pre><code>id   event_sequnce
  1    a-&gt;c-&gt;b-&gt;c-&gt;b
  2    d-&gt;a-&gt;d-&gt;c-&gt;a-&gt;c
  </code></pre>
  
  <p>How to write query to achieve this?</p>