MySQL - Select all rows where a field value is not unique

Question

How can I select all rows in MySQL where a particular field value is not unique. For example I have the following data:

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| ID | Name   |         URL           |
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| 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 |
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In this I would want to return the following where the URL field has duplicates:

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| ID | Name   |         URL           |
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| 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 |
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Answer 1

or, old school...

SELECT DISTINCT x.* 
           FROM my_table x 
           JOIN my_table y 
             ON y.url = x.url 
            AND y.id <> x.id 
          ORDER 
             BY id;