mysql group by join列太慢

Question

我有两个表events和event_params

第一个表使用这些列存储事件

events | CREATE TABLE `events` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `project` varchar(24) NOT NULL,
  `event` varchar(24) NOT NULL,
  `date` int(10) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  KEY `project` (`project`,`event`)
) ENGINE=InnoDB AUTO_INCREMENT=2915335 DEFAULT CHARSET=latin1

第二个使用这些列存储每个事件的参数

event_params | CREATE TABLE `event_params` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `event_id` int(10) unsigned NOT NULL,
  `name` varchar(24) NOT NULL,
  `value` varchar(524) CHARACTER SET utf8 NOT NULL,
  PRIMARY KEY (`id`),
  KEY `name` (`name`),
  KEY `event_id` (`event_id`),
  KEY `value` (`value`),
) ENGINE=InnoDB AUTO_INCREMENT=20789391 DEFAULT CHARSET=latin1

现在我想获取在指定参数上具有各种值的事件计数

我为campaign参数编写了此查询，但这太慢了（响应时间为15秒）

SELECT
    event_params.value as campaign,
    count(*) as count
FROM `events`
    left join event_params on event_params.event_id = events.id
                          and event_params.name = 'campaign'
WHERE events.project = 'foo'
GROUP by event_params.value

这是EXPLAIN查询结果：

+----+-------------+--------------+------------+------+---------------------+----------+---------+------------------+------+----------+----------------------------------------------+
| id | select_type | table        | partitions | type | possible_keys       | key      | key_len | ref              | rows | filtered | Extra                                        |
+----+-------------+--------------+------------+------+---------------------+----------+---------+------------------+------+----------+----------------------------------------------+
|  1 | SIMPLE      | events       | NULL       | ref  | project             | project  | 26      | const            |    1 |   100.00 | Using index; Using temporary; Using filesort |
|  1 | SIMPLE      | event_params | NULL       | ref  | name,event_id,value | event_id | 4       | events.events.id |    4 |   100.00 | Using where                                  |
+----+-------------+--------------+------------+------+---------------------+----------+---------+------------------+------+----------+----------------------------------------------+

我可以加快查询速度吗？

Answer 1

您可以尝试在event_params表上添加以下索引，这可以加快连接速度：

CREATE INDEX idx1 ON event_params (event_id, name, value);

由于COUNT操作涉及对每个记录进行计数，因此可能无法对聚合步骤进行太多优化。

Answer 2

将“广告系列值”移动到主表中，并为VARCHAR输入合适的长度，然后

SELECT
    campaign,
    count(*) as count
FROM `events`
WHERE project = 'foo'
GROUP by campaign

并有

INDEX(project, campaign)

尝试使用EAV时的一些建议：将“重要”值移到主表中； 在另一个表中只保留很少使用或很少设置的“值”。 另外（假设没有公仔），有

PRIMARY KEY(event_id, name)

更多讨论： http : //mysql.rjweb.org/doc.php/eav