Question

考虑此查询：

select d.*
from data d
where channel_id=83
order by channel_id,timestamp

执行立即执行，因为channel_id，时间戳被索引：

CREATE TABLE `data` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `channel_id` int(11) DEFAULT NULL,
  `timestamp` bigint(20) NOT NULL,
  `value` double NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `data_unique` (`channel_id`,`timestamp`),
  KEY `IDX_ADF3F36372F5A1AA` (`channel_id`),
  CONSTRAINT `FK_ADF3F36372F5A1AA` FOREIGN KEY (`channel_id`) REFERENCES `entities` (`id`)
)

一旦我添加了一个简单的LAG（），查询就会变得缓慢：

select d.*
,lag(value) over (order by channel_id,timestamp)
from data d
where channel_id=83
order by channel_id,timestamp

说明计划：

+------+-------------+-------+------+----------------------------------+----------------------+---------+-------+--------+-----------------+
| id   | select_type | table | type | possible_keys                    | key                  | key_len | ref   | rows   | Extra           |
+------+-------------+-------+------+----------------------------------+----------------------+---------+-------+--------+-----------------+
|    1 | SIMPLE      | d     | ref  | data_unique,IDX_ADF3F36372F5A1AA | IDX_ADF3F36372F5A1AA | 5       | const | 759654 | Using temporary |
+------+-------------+-------+------+----------------------------------+----------------------+---------+-------+--------+-----------------+

在没有LAG（）语句的情况下说明计划：

+------+-------------+-------+------+----------------------------------+----------------------+---------+-------+--------+-------+
| id   | select_type | table | type | possible_keys                    | key                  | key_len | ref   | rows   | Extra |
+------+-------------+-------+------+----------------------------------+----------------------+---------+-------+--------+-------+
|    1 | SIMPLE      | d     | ref  | data_unique,IDX_ADF3F36372F5A1AA | IDX_ADF3F36372F5A1AA | 5       | const | 759730 |       |
+------+-------------+-------+------+----------------------------------+----------------------+---------+-------+--------+-------+

mariadb中的窗口函数是否存在性能问题，还是我的查询错误？

MariaDB中的窗口功能是否很慢？

0 个答案: