我有3个表格，其中包含以下架构：
CREATE TABLE `devices` (
`device_id` int(11) NOT NULL auto_increment,
`name` varchar(20) default NULL,
`appliance_id` int(11) default '0',
`sensor_type` int(11) default '0',
`display_name` VARCHAR(100),
PRIMARY KEY USING BTREE (`device_id`)
)
CREATE TABLE `channels` (
`channel_id` int(11) NOT NULL AUTO_INCREMENT,
`device_id` int(11) NOT NULL,
`channel` varchar(10) NOT NULL,
PRIMARY KEY (`channel_id`),
KEY `device_id_idx` (`device_id`)
)
CREATE TABLE `historical_data` (
`date_time` datetime NOT NULL,
`channel_id` int(11) NOT NULL,
`data` float DEFAULT NULL,
`unit` varchar(10) DEFAULT NULL,
KEY `devices_datetime_idx` (`date_time`) USING BTREE,
KEY `channel_id_idx` (`channel_id`)
)
设置是设备可以有一个或多个通道，每个通道都有许多（历史）数据。
我使用以下查询来获取一个设备及其所有相关频道的最新历史数据：
SELECT c.channel_id, c.channel, max(h.date_time), h.data
FROM devices d
INNER JOIN channels c ON c.device_id = d.device_id
INNER JOIN historical_data h ON h.channel_id = c.channel_id
WHERE d.name = 'livingroom' AND d.appliance_id = '0'
AND d.sensor_type = 1 AND ( c.channel = 'ch1')
GROUP BY c.channel
ORDER BY h.date_time, channel
查询计划如下所示：
+----+-------------+-------+--------+-----------------------+----------------+---------+---------------------------+--------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+-----------------------+----------------+---------+---------------------------+--------+-------------+
| 1 | SIMPLE | c | ALL | PRIMARY,device_id_idx | NULL | NULL | NULL | 34 | Using where |
| 1 | SIMPLE | d | eq_ref | PRIMARY | PRIMARY | 4 | c.device_id | 1 | Using where |
| 1 | SIMPLE | h | ref | channel_id_idx | channel_id_idx | 4 | c.channel_id | 322019 | |
+----+-------------+-------+--------+-----------------------+----------------+---------+---------------------------+--------+-------------+
3 rows in set (0.00 sec)
上述查询目前大约需要15秒，我想知道是否有任何提示或方法可以改进查询？
编辑： 来自historical_data的示例数据
+---------------------+------------+------+------+
| date_time | channel_id | data | unit |
+---------------------+------------+------+------+
| 2011-11-20 21:30:57 | 34 | 23.5 | C |
| 2011-11-20 21:30:57 | 9 | 68 | W |
| 2011-11-20 21:30:54 | 34 | 23.5 | C |
| 2011-11-20 21:30:54 | 5 | 316 | W |
| 2011-11-20 21:30:53 | 34 | 23.5 | C |
| 2011-11-20 21:30:53 | 2 | 34 | W |
| 2011-11-20 21:30:51 | 34 | 23.4 | C |
| 2011-11-20 21:30:51 | 9 | 68 | W |
| 2011-11-20 21:30:49 | 34 | 23.4 | C |
| 2011-11-20 21:30:49 | 4 | 193 | W |
+---------------------+------------+------+------+
10 rows in set (0.00 sec)
编辑2： 多个通道SELECT示例：
SELECT c.channel_id, c.channel, max(h.date_time), h.data
FROM devices d
INNER JOIN channels c ON c.device_id = d.device_id
INNER JOIN historical_data h ON h.channel_id = c.channel_id
WHERE d.name = 'livingroom' AND d.appliance_id = '0'
AND d.sensor_type = 1 AND ( c.channel = 'ch1' OR c.channel = 'ch2' OR c.channel = 'ch2')
GROUP BY c.channel
ORDER BY h.date_time, channel
我在c.channel where子句中使用了OR，因为它更容易以编程方式生成，但如果需要可以更改为使用IN。
编辑3： 我想要实现的结果的示例结果：
+-----------+------------+---------+---------------------+-------+
| device_id | channel_id | channel | max(h.date_time) | data |
+-----------+------------+---------+---------------------+-------+
| 28 | 9 | ch1 | 2011-11-21 20:39:36 | 0 |
| 28 | 35 | ch2 | 2011-11-21 20:30:55 | 32767 |
+-----------+------------+---------+---------------------+-------+
我已将device_id添加到示例中，但我的选择只需返回channel_id，channel，last date_time，即max和数据。结果应该是一个设备的每个通道的historical_data表中的最后一条记录。
答案 0 :(得分：1)
似乎删除了在date_time上重新创建索引，通过删除并再次创建它，加快了我的原始SQL，大约2秒
答案 1 :(得分：0)
我无法对此进行测试，所以我想请你运行它，让我们知道会发生什么......如果它能给你想要的结果，并且它的运行速度比你当前的速度快：
CREATE DEFINER=`root`@`localhost` PROCEDURE `GetLatestHistoricalData_EXAMPLE`
(
IN param_device_name VARCHAR(20)
, IN param_appliance_id INT
, IN param_sensor_type INT
, IN param_channel VARCHAR(10)
)
BEGIN
SELECT
h.date_time, h.data
FROM
historical_data h
INNER JOIN
(
SELECT c.channel_id
FROM devices d
INNER JOIN channels c ON c.device_id = d.device_id
WHERE
d.name = param_device_name
AND d.appliance_id = param_appliance_id
AND d.sensor_type = param_sensor_type
AND c.channel = param_channel
)
c ON h.channel_id = c.channel_id
ORDER BY h.date_time DESC
LIMIT 1;
END
然后进行测试：
CALL GetLatestHistoricalData_EXAMPLE ('livingroom', 0, 1, 'ch1');
我尝试将其用于存储过程，以便即使您使用此设备获得所需的结果，也可以使用其他设备尝试并查看结果...谢谢！
[edit] ::响应Danny的评论，这是一个更新的测试版本：
CREATE DEFINER=`root`@`localhost` PROCEDURE `GetLatestHistoricalData_EXAMPLE_3Channel`
(
IN param_device_name VARCHAR(20)
, IN param_appliance_id INT
, IN param_sensor_type INT
, IN param_channel_1 VARCHAR(10)
, IN param_channel_2 VARCHAR(10)
, IN param_channel_3 VARCHAR(10)
)
BEGIN
SELECT
h.date_time, h.data
FROM
historical_data h
INNER JOIN
(
SELECT c.channel_id
FROM devices d
INNER JOIN channels c ON c.device_id = d.device_id
WHERE
d.name = param_device_name
AND d.appliance_id = param_appliance_id
AND d.sensor_type = param_sensor_type
AND (
c.channel IN (param_channel_1
,param_channel_2
,param_channel_3
)
c ON h.channel_id = c.channel_id
ORDER BY h.date_time DESC
LIMIT 1;
END
然后进行测试：
CALL GetLatestHistoricalData_EXAMPLE_3Channel ('livingroom', 0, 1, 'ch1', 'ch2' , 'ch3');
同样，这仅用于测试，因此您将能够看到它是否满足您的需求..
答案 2 :(得分：0)
我首先在设备表（appliance_id，sensor_type，name）上添加一个索引以匹配您的查询。我不知道这个表中有多少条目，但是如果大，每个设备有很多元素，那么就可以了。
其次，在您的频道表上，索引（device_id，频道）
第三，关于你的历史数据，索引（channel_id，date_time）
然后，
SELECT STRAIGHT_JOIN
PreQuery.MostRecent,
PreQuery.Channel_ID,
PreQuery.Channel,
H2.Data,
H2.Unit
from
( select
c.channel_id,
c.channel,
max( h.date_time ) as MostRecent
from
devices d
join channels c
on d.device_id = c.device_id
and c.channel in ( 'ch1', 'ch2', 'ch3' )
join historical_data h
on c.channel_id = c.Channel_id
where
d.appliance_id = 0
and d.sensor_type = 1
and d.name = 'livingroom'
group by
c.channel_id ) PreQuery
JOIN Historical_Data H2
on PreQuery.Channel_ID = H2.Channel_ID
AND PreQuery.MostRecent = H2.Date_Time
order by
PreQuery.MostRecent,
PreQuery.Channel