title: SQL selecting earliest date of subgroup
body: <p>I have a table which looks like the following:</p>
  
  <hr>
  
  <p>| ID | Person | Modified On |</p>
  
  <hr>
  
  <p>If I have the following records: </p>
  
  <p><code>{id: 1, person: 'John', Modified On: 2014-06-01 12:00:00},
  {id: 2, person 'John', Modified On: 2014-06-02 12:00:00},
  {id: 2, person 'Kate', Modified On: 2014-06-02 12:08:00},
  {id: 2, person 'Sarah', Modified On: 2014-06-02 12:02:00},
  {id: 2, person 'Sarah', Modified On: 2014-06-01 12:00:00}
  </code></p>
  
  <p>Notice that the same person "John" and Sarah is in there twice.  Modified once on June 1, and again on June 2.  </p>
  
  <p>What I'd like is to be able to select one of each person, but only their earliest dates.  So my results should be:</p>
  
  <p><code>{id: 1, person: 'John', Modified On: 2014-06-01 12:00:00},
  {id: 2, person 'Kate', Modified On: 2014-06-02 12:08:00},
  {id: 2, person 'Sarah', Modified On: 2014-06-01 12:00:00}
  </code></p>
  
  <p>How should I construct my SQL to do so?</p>