title: Alter a nonunique index to a unique index
body: <p>I have a few non-unique constraints that I want to alter into unique constraints ( business rules have changed since the data model was made ).  Is there any way to do it with out dropping and recreating as a unique constraint?  I was thinking there would be an option in the <code>alter constraint</code> command, but I have not found anything.</p>
  
  <p>Thanks!! </p>