title: Oracle SQL SUBSTR function
body: <p>I have a table like below:</p>
  
  <pre><code>Last_name First_name
  aaaa       bbb -
  aaa        bbbb -
  aaa        gggg j
  </code></pre>
  
  <p>How can I use substr function to delete the - in the <code>first_name</code> and keep the letter if it is not a -?</p>
  
  <p>Thanks</p>