title: Decrement value in mysql but not negative
body: <p>I want to decrement a value when user delete it in php and mysql. I want to check not to go below than 0. If value is 0 then do not <strong>decrement</strong>.</p>
  
  <pre><code>mysql_query("UPDATE table SET field = field - 1 WHERE id = $number");
  </code></pre>
  
  <p>If field is <strong>0</strong> then do not do anything</p>