mysql group by join列太慢

Question

我有兩個表events和event_params

第一個表使用這些列存儲事件

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

第二個使用這些列存儲每個事件的參數

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

現在我想獲取在指定參數上具有各種值的事件計數

我為campaign參數編寫了此查詢，但這太慢了（響應時間為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

這是EXPLAIN查詢結果：

+----+-------------+--------------+------------+------+---------------------+----------+---------+------------------+------+----------+----------------------------------------------+
| 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                                  |
+----+-------------+--------------+------------+------+---------------------+----------+---------+------------------+------+----------+----------------------------------------------+

我可以加快查詢速度嗎？

Answer 1

您可以嘗試在event_params表上添加以下索引，這可以加快連接速度：

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

由於COUNT操作涉及對每個記錄進行計數，因此可能無法對聚合步驟進行太多優化。

Answer 2

將“廣告系列值”移動到主表中，並為VARCHAR輸入合適的長度，然后

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

並有

INDEX(project, campaign)

嘗試使用EAV時的一些建議：將“重要”值移到主表中； 在另一個表中只保留很少使用或很少設置的“值”。 另外（假設沒有公仔），有

PRIMARY KEY(event_id, name)

更多討論： http : //mysql.rjweb.org/doc.php/eav