title: mysql random generated value
body: <p>I need to generate a random alpha/numeric to give to users that they come to the site to enter.  I dont' know much about random numbers and such, I know there are seeding issues and such, but I'm not sure what they are.</p>
  
  <p>So, I used this:</p>
  
  <blockquote>
    <p>select    substrING(md5(concat_ws('-',md5(username_usr),
    MD5(zip_usr), MD5(id_usr),
    MD5(created_usr))),-12) from users_usr</p>
  </blockquote>
  
  <p>Is this safe? I used concat_ws because sometimes zip is null, but the others never are.</p>
  
  <p>And yes, I know this is kinda short, but 1. They have to enter the last 4 of their social, 2. It's 1 time use, 3. There's no private data displayed back in the application and 4. I may use captcha, but since there's no private data, thats probably overkill.</p>
  
  <p>THanks</p>