title: Create a new column based on other columns
body: <p>I've managed to create the following column in a new table: </p>
  
  <pre><code>CREATE TABLE t_issue_dates as
  
  SELECT issue_d,
  
  cast(substr(issue_d,5,4) as numeric) as issue_year
  FROM myDB
  </code></pre>
  
  <p>(The code recodes a year-month variable to a year-only variable)</p>
  
  <p>However, i can't add this variable to my existing table "myDB". I've tried using the:</p>
  
  <p><code>ALTER TABLE myDB ADD v_year</code> - command, but i can't manage to get it right. </p>
  
  <p>Does anyone have an idea how i add the above variable to the "original" table myDB?</p>
  
  <p>Thank you!</p>