title: How to generate unique id in MySQL?
body: <p>I'm programming a script using PHP and MySQL and I want to get a 
  unique id (consisting of a string: capitals and small 
  letters with numbers) like: <code>gHYtUUi5b</code>.
  I found many functions in PHP that can generate such numbers but I'm afraid about how to ensure the id is unique!</p>
  
  <p><strong>UPDATE</strong>: uuid is long, I mean such id like: (P5Dc) an 11 alphanumeric char.</p>