title: Still show the proper set of time even if there's no entry for that time
body: <p>I have this query where it gets the average and group the values by 15 mins from 12 AM to 11:45 PM.</p>
  
  <pre><code>SELECT FROM_UNIXTIME(t_stamp/1000, '%m/%d/%Y %l:%i %p') as t_stamp,
      ROUND(AVG(CASE WHEN id = '001' THEN value END),2) Value1,   
      ROUND(AVG(CASE WHEN id = '002' THEN value END),2) Value2,
      ROUND(AVG(CASE WHEN id = '003' THEN value END),2) Value3
  
  FROM table1
  WHERE tagid IN ("001", "002", "003") and
  
  date(from_unixtime(t_stamp/1000)) BETWEEN "2014-05-01" AND "2014-05-01"
  
  GROUP BY DATE(from_unixtime(t_stamp/1000)), HOUR(from_unixtime(t_stamp/1000)), MINUTE(from_unixtime(t_stamp/1000))  DIV 15
  </code></pre>
  
  <p>The output looks like this</p>
  
  <pre><code>    t_stamp             |   Value1  |   Value2  |   Value3
  05/01/2014 12:00 AM     |   199     |   99      |   100
  05/01/2014 12:15 AM     |   299     |   19      |   140
  05/01/2014 12:30 AM     |   399     |   59      |   106
  05/01/2014 12:45 AM     |   499     |   59      |   112
  .
  .
  .
  05/01/2014 11:00 PM     |   149     |   199     |   100
  05/01/2014 11:15 PM     |   599     |   93      |   123
  05/01/2014 11:30 PM     |   129     |   56      |   150
  05/01/2014 11:45 PM     |   109     |   60      |   134
  </code></pre>
  
  <p>It works fine but I've noticed that sometimes if there's no entry for like the time 12:30 instead of showing</p>
  
  <pre><code>    t_stamp             |   Value1  |   Value2  |   Value3
  05/01/2014 12:00 AM     |   199     |   99      |   100
  05/01/2014 12:15 AM     |   299     |   19      |   140
  05/01/2014 12:30 AM     |   Null    |   Null    |   Null
  05/01/2014 12:45 AM     |   499     |   59      |   112
  </code></pre>
  
  <p>It will show the set of time like this:</p>
  
  <pre><code>    t_stamp             |   Value1  |   Value2  |   Value3
  05/01/2014 12:00 AM     |   199     |   99      |   100
  05/01/2014 12:15 AM     |   299     |   19      |   140
  05/01/2014 12:33 AM     |   122     |   141     |   234
  05/01/2014 12:45 AM     |   499     |   59      |   112
  </code></pre>
  
  <p>What I would like to happen is when there's no time for that 15 min group it will still show the proper set of time and then just show null on the column values. The output I would like is like this:</p>
  
  <pre><code>    t_stamp             |   Value1  |   Value2  |   Value3
  05/01/2014 12:00 AM     |   199     |   99      |   100
  05/01/2014 12:15 AM     |   299     |   19      |   140
  05/01/2014 12:30 AM     |   Null    |   Null    |   Null
  05/01/2014 12:45 AM     |   499     |   59      |   112
  </code></pre>
  
  <p>How can I do this?</p>
  
  <p>Thank You.</p>