title: Selecting dates when column value changes
body: <p>I have a table like this</p>
  
  <pre><code>| ID | CAMPAIGN_ID | CHARGES |                            DATE |
  ----------------------------------------------------------------
  |  1 |           1 |      15 | November, 17 2012 09:53:08+0000 |
  |  2 |           1 |      15 | November, 18 2012 09:53:08+0000 |
  |  3 |           1 |      15 | November, 22 2012 09:53:08+0000 |
  |  4 |           1 |      15 | November, 24 2012 09:53:08+0000 |
  |  5 |           1 |      15 | November, 26 2012 09:53:08+0000 |
  |  6 |           1 |      10 | November, 27 2012 09:53:08+0000 |
  |  7 |           1 |      10 | November, 28 2012 09:53:08+0000 |
  |  8 |           1 |      10 | December, 02 2012 09:53:08+0000 |
  |  9 |           1 |      10 | December, 04 2012 09:53:08+0000 |
  | 10 |           1 |      10 | December, 05 2012 09:53:08+0000 |
  | 11 |           1 |      10 | December, 06 2012 09:53:08+0000 |
  | 12 |           1 |      10 | December, 07 2012 09:53:08+0000 |
  | 13 |           1 |      15 | December, 08 2012 09:53:08+0000 |
  | 14 |           1 |      15 | December, 09 2012 09:53:08+0000 |
  | 15 |           1 |      15 | December, 10 2012 09:53:08+0000 |
  | 16 |           1 |      15 | December, 12 2012 09:53:08+0000 |
  | 17 |           1 |      15 | December, 13 2012 09:53:08+0000 |
  </code></pre>
  
  <p><a href="http://sqlfiddle.com/#!2/89b89/1" rel="nofollow">SQL Fiddle Schema</a></p>
  
  <p>I want to select the dates on which the charges are being changing. The output is here</p>
  
  <pre><code>| ID | CAMPAIGN_ID | CHARGES |                            DATE |
  ----------------------------------------------------------------
  |  6 |           1 |      10 | November, 27 2012 09:53:08+0000 |
  | 13 |           1 |      15 | December, 08 2012 09:53:08+0000 |
  </code></pre>
  
  <p>How can i achieve this with mysql.</p>