title: Best way for Unique Random String for MySQL Long table
body: <p>I know how to create random chars both at PHP and MySQL but the question is that I have to create a 4 char random string for a table of 10 thousand or so rows. What way is the best to make sure it will remain unique?</p>
  
  <p>I can use a longer string if I need to but not longer then 12.</p>
  
  <p>Just to make it simple, table exists I need to add an extra column and fill it with a 4 char random string and keys must remain unique.</p>