title: ADD 7 days to string formatted date
body: <p>I have a varchar date in my table formatted as 20060918 and I want to be able to add 7 days to this date, and keep it valid (it would give me an invalid date if I tried to just +7)
  This is my code</p>
  
  <pre><code>SELECT cast (WD.Adjusted_Hire_Date as date format 'YYYY-MM-DD')+ INTERVAL '7' DAY
  from Analytics.Workday as WD;
  </code></pre>
  
  <p>but I'm getting an error </p>
  
  <pre><code>Executed as Single statement.  Failed [2666 : 22007] Invalid date supplied for Workday.Adjusted_Hire_Date. 
  </code></pre>
  
  <p>Should I convert the Adjusted_Hire_Date column before?</p>