title: PHP - uniqid("",true) versus uniqid("")+mt_rand()
body: <p>What are the key differences between these two approaches to generate sequential-but-somewhat-unique numbers?  I want to use such a number as a unique user ID inside a MySQL db, and also as a salt to salt a password.</p>
  
  <p>My understanding is that for clustering and indexing reasons those IDs should be sequential (I realize that in some cases the random string will make two entries that occurred in the same microsecond non sequential, but hopefully this is negligible.)</p>