title: How to define a deferred constraint in MySQL
body: <p>is it possible to create a primary key in a existing table on a column that have repeated value? I want is previous record not validate but new record will validate with this.Is it possible in mysql. I know it is possible in Oracle (<a href="http://www.oracle-base.com/articles/8i/constraint-checking-updates.php" rel="nofollow">here is an example</a>) but don't have idea about mysql. </p>