title: How to change column entries in Q/KDB
body: <p>I have a table named Pnl having many columns, one of them is Tenor with following entries:</p>
  
  <pre><code>**Tenor**
  
  5y
  
  10y
  
  20y
  
  10Y
  
  5Y
  
  25Y
  
  20y
  </code></pre>
  
  <p>How can I modify these rows in q/kdb such that 'y' &amp; 'Y' become similar? 
  I tried converting atoms into strings using <code>string</code>Tenor but it doesn't work for a column.</p>