title: adding a sort-key in aws redshift
body: <p>How to alter an already existing column in aws redshit to make it a sort-key?</p>
  
  <p>like I have a column username in table users and I want to make it a sortkey</p>
  
  <p>is there an sql query for this like:</p>
  
  <p><strong>"alter table users add sortkey(username)"</strong></p>
  
  <p>Thanks in advance.</p>