I could not find documentation on this specific matter, either in the documentation for <code>UPDATE</code> or in the documentation for <code>CREATE TRIGGER</code>. And if it makes sense both ways, and it's not documented, it can change. Once again I recommend that if you want to know how many rows will be found by an <code>UPDATE</code> you execute the equivalent <code>SELECT</code> and count the rows returned (or use <code>COUNT(*)</code>).