title: MySQL innodb: Safe to rely on default order when using LIMIT?
body: <p>I use an innodb table to store contact information. 
  I display data paginated. The query for the first page looks like this:</p>
  
  <pre><code>SELECT name, email FROM contacts WHERE userid = 1 LIMIT 0,50
  </code></pre>
  
  <p>The column email in compound with userid is the primary key, so the result is sorted by it by default. 
  The query for the second page looks like this;</p>
  
  <pre><code>SELECT name, email FROM contacts WHERE userid = 1 LIMIT 50,50
  </code></pre>
  
  <p>Now my question: Is it safe to rely on the default sorting order of innodb (I know I could simply add <code>ORDER BY email</code> To make sure)?
  In other words, is it possible that the same contacts might be shown on page one and on page two? What would that depend on?</p>