title: execute constraint on update sql
body: <p>I have a constraint that return datetime for a column (date). 
  On insert work it! Now I would like update column date with new value of getdate() when an update statement execute.  Any idea? </p>
  
  <p>My constraint:</p>
  
  <pre><code>ALTER TABLE [tablename] ADD CONSTRAINT [constraintName]
  DEFAULT (getdate()) FOR [column]
  </code></pre>
  
  <p>MY DBMS is Microsoft SQL Server 2012</p>