title: MySQL: Updatable VIEW with derived column; Equivalent functionality of "INSTEAD OF UPDATE" Trigger
body: <p>I would like to have a view that has a derived column.  For example I have a table with fields: Qty and Price.  My view then has those fields as well as a calculated field Qty*Price.</p>
  
  <p>I'm using MySQL.  As I understand it, MySQL doesn't allow the view to be editable if there is a derived table (Updatable and Insertable Views -- <a href="http://dev.mysql.com/doc/refman/5.0/en/view-updatability.html" rel="nofollow noreferrer">http://dev.mysql.com/doc/refman/5.0/en/view-updatability.html</a>).  </p>
  
  <p>When I was working with sqlite, I was able to get around this by creating an "INSTEAD OF UPDATE" trigger (for example see <a href="https://stackoverflow.com/a/4507202/1029698">this</a> stackoverflow response).  However, MySQL apparently doesn't allow this type of trigger.  (MySQL Trigger Syntax -- <a href="http://dev.mysql.com/doc/refman/5.0/en/create-trigger.html" rel="nofollow noreferrer">http://dev.mysql.com/doc/refman/5.0/en/create-trigger.html</a>)</p>
  
  <p>Are there any other ways I could get this kind of functionality with MySQL -- namely a view with a derived column that is also editable?  Obviously, I can do it on the application side without the view, but I would much prefer it on the DB side if possible.</p>