title: MySQL - Select all rows where a field value is not unique
body: <p>How can I select all rows in MySQL where a particular field value is not unique. For example I have the following data:</p>
  
  <pre><code>---------------------------------------
  | ID | Name   |         URL           |
  ---------------------------------------
  | 1  | Store 1| http://www.store1.com |
  | 2  | Store 2| http://www.store1.com |
  | 3  | Store 3| http://www.store3.com |
  | 4  | Store 4| http://www.store4.com |
  | 5  | Store 5| http://www.store4.com |
  ---------------------------------------
  </code></pre>
  
  <p>In this I would want to return the following where the URL field has duplicates:</p>
  
  <pre><code>---------------------------------------
  | ID | Name   |         URL           |
  ---------------------------------------
  | 1  | Store 1| http://www.store1.com |
  | 2  | Store 2| http://www.store1.com |
  | 4  | Store 4| http://www.store4.com |
  | 5  | Store 5| http://www.store4.com |
  ---------------------------------------
  </code></pre>