sampling data

SELECT
 DATE_FORMAT( FROM_UNIXTIME(UNIX_TIMESTAMP(time) - UNIX_TIMESTAMP(time)%(15*60) )
 , '%H:%i %s') AS S_TIME
 , time
 from a;
 -----------------------------------------------------------------------------------------------

 SELECT
 DATE_FORMAT( FROM_UNIXTIME(UNIX_TIMESTAMP(time) - UNIX_TIMESTAMP(time)%(1*60) )
 , '%H:%i %s') AS S_TIME
 , min(val)
 , max(val)
 , avg(val)
 , count(*)
 from a
 group by s_time
 ;


SELECT
 DATE_FORMAT( FROM_UNIXTIME(UNIX_TIMESTAMP(time) - UNIX_TIMESTAMP(time)%(3) )
 , '%H:%i %s') AS S_TIME
 , time
 from a;


 ---------------------------------------------------------------------------------
 mysql> SELECT
    ->  DATE_FORMAT( FROM_UNIXTIME(UNIX_TIMESTAMP(time) - UNIX_TIMESTAMP(time)%(3) )
    ->  , '%H:%i %s') AS S_TIME
    ->  , time
    ->  from a;
+----------+----------------+
| S_TIME   | time           |
+----------+----------------+
| 15:00 00 | 20140318150000 |
| 15:00 00 | 20140318150001 |
| 15:00 00 | 20140318150002 |
| 15:00 03 | 20140318150003 |
| 15:00 03 | 20140318150004 |
| 15:00 03 | 20140318150005 |
| 15:00 06 | 20140318150006 |
| 15:00 06 | 20140318150007 |
| 15:00 06 | 20140318150008 |
| 15:00 09 | 20140318150009 |
| 15:00 09 | 20140318150010 |
| 16:00 00 | 20140318160001 |
| 16:00 00 | 20140318160002 |
| 16:30 00 | 20140318163001 |
| 16:40 00 | 20140318164001 |
| 16:50 00 | 20140318165001 |
| 16:51 00 | 20140318165101 |
| 16:52 00 | 20140318165201 |
| 16:53 00 | 20140318165301 |
| 16:54 00 | 20140318165401 |
| 16:55 00 | 20140318165501 |
| 16:56 00 | 20140318165601 |
| 16:57 00 | 20140318165701 |
| 16:58 00 | 20140318165801 |
| 16:59 00 | 20140318165901 |
| 17:00 00 | 20140318170000 |
| 16:45 00 | 20140318164500 |
| 16:44 00 | 20140318164400 |
+----------+----------------+
28 rows in set (0.00 sec)