в дополнение к обычному использованию GROUP BY и AVG() вас может заинтересовать ответ Quassnoi на мой вопрос здесь:
GROUP BY для непрерывных строк в SQL
Он опубликовал очень хорошее решение, которое также очень хорошо работает со многими строками.
Думайте о скорости как о состоянии, и вы хотите объединить все непрерывные строки за период времени с одинаковой скоростью.
Вот моя попытка переписать ваш запрос, используя этот метод:
SELECT
UNITID,
/* we aggregate multiple rows, maybe you want to know which ones..
this one is optional */
CAST(GROUP_CONCAT(UUID SEPARATOR ', ') AS CHAR) AS UUIDS,
/* is group field in the inner subquery, we can just use it
in our select without an aggregate function */
SPEED,
/* very important to select the lowest timestamp -
this is the time when your unit has stopped moving ..
first row with speed=0 */
MIN(TRACKINGTIME) AS TRACKINGTIME,
/* we calc the average on latitude here */
TRUNCATE(AVG(LATITUDE),6) AS LATITUDE,
/* same for longitude */
TRUNCATE(AVG(LONGITUDE),6) AS LONGITUDE,
/* maybe you want to know how many rows with speed 0
are grouped together */
COUNT(UUID) AS AGGREGATE_COUNT
FROM (
SELECT
/* this increases the counter variable @r each time
the state has changed.. when speed of the previous row
was also "0" and is "0" in the current row,
the counter is not increased. -- this is a virtual field
we will use for GROUPing.
@speed is used to remember the speed of the previous
row for comparison in @r to determine if the speed has changed
*/
@r := @r + (@prev_unit != UNITID
OR @prev_speed != 0
OR SPEED != 0) AS gn,
@prev_speed := SPEED AS a_speed,
@prev_unit := UNITID AS a_unit,
tp.*
FROM (
SELECT @r := 0,
@prev_speed := 1,
@prev_unit := ''
) vars,
trackpoint_au tp
ORDER BY
UNITID, TRACKINGTIME
) q
GROUP BY
gn
ORDER BY
UNITID
Тестовые данные:
CREATE TABLE `trackpoint_au` (
`uuid` int(11) NOT NULL AUTO_INCREMENT,
`latitude` decimal(10,0) NOT NULL,
`longitude` decimal(10,0) NOT NULL,
`speed` int(11) NOT NULL,
`unitid` int(11) NOT NULL,
`trackingtime` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`uuid`)
) ENGINE=MyISAM;
INSERT INTO trackpoint_au (unitid, speed, latitude, longitude, trackingtime) VALUES
(1, 0, 10, 10, NOW()),
(1, 0, 20, 20, NOW()),
(1, 1, 10, 10, NOW()),
(1, 0, 10, 10, NOW()),
(1, 0, 30, 30, NOW()),
(2, 0, 10, 10, NOW()),
(2, 0, 20, 20, NOW()),
(3, 1, 10, 10, NOW()),
(4, 0, 10, 10, NOW()),
(4, 0, 20, 20, NOW()),
(4, 1, 30, 30, NOW()),
(4, 0, 60, 60, NOW()),
(4, 0, 60, 60, NOW());
Результат:
+--------+--------+-------+---------------------+-----------+-----------+-----------------+
| UNITID | UUIDS | SPEED | TRACKINGTIME | LATITUDE | LONGITUDE | AGGREGATE_COUNT |
+--------+--------+-------+---------------------+-----------+-----------+-----------------+
| 1 | 2, 1 | 0 | 2011-12-05 09:34:13 | 15.000000 | 15.000000 | 2 |
| 1 | 3 | 1 | 2011-12-05 09:34:13 | 10.000000 | 10.000000 | 1 |
| 1 | 4, 5 | 0 | 2011-12-05 09:34:13 | 20.000000 | 20.000000 | 2 |
| 2 | 6, 7 | 0 | 2011-12-05 09:34:13 | 15.000000 | 15.000000 | 2 |
| 3 | 8 | 1 | 2011-12-05 09:34:13 | 10.000000 | 10.000000 | 1 |
| 4 | 9, 10 | 0 | 2011-12-05 09:34:13 | 15.000000 | 15.000000 | 2 |
| 4 | 11 | 1 | 2011-12-05 09:34:13 | 30.000000 | 30.000000 | 1 |
| 4 | 12, 13 | 0 | 2011-12-05 09:34:13 | 60.000000 | 60.000000 | 2 |
+--------+--------+-------+---------------------+-----------+-----------+-----------------+