title: Data Transformation to convert one row into multiple rows
body: <p>I do have a table which has the data as shown below.</p>
  
  <pre><code>Table_A
  
  Row Id    Date1        Date2        Date3
  1         1/12/2008    2/12/2008    3/12/2008
  2         2/12/2010    NULL          NULL
  3         3/12/2008    4/12/2008     NULL
  </code></pre>
  
  <p>I need to write a MySQL query to get result like this</p>
  
  <pre><code>Row Id    App_Date     Date1          Date2         Date3
  1         1/12/2008    1/12/2008      2/12/2008     3/12/2008
  1         2/12/2008    1/12/2008      2/12/2008     3/12/2008
  1         3/12/2008    1/12/2008      2/12/2008     3/12/2008
  2         2/12/2010    2/12/2010      NULL          NULL
  3         3/12/2008    3/12/2008      4/12/2008     NULL
  3         4/12/2008    3/12/2008      4/12/2008     NULL
  </code></pre>
  
  <p>Basically I want to populate a new column <code>App_Date</code> based on <code>Date1</code>, <code>Date2</code> and <code>Date3</code>. If any of the Date fields has any value. </p>
  
  <p>Then I should create a record with the date populated in that column. For instance, if all the 3 dates populated on a record, I should have 3 records for that one record with the date populated in the new column <code>App_Date</code> like above. </p>
  
  <p>What is the most optimal MySQL query to achieve this?</p>