作者热门文章
- html - 出于某种原因,IE8 对我的 Sass 文件中继承的 html5 CSS 不友好?
- JMeter 在响应断言中使用 span 标签的问题
- html - 在 :hover and :active? 上具有不同效果的 CSS 动画
- html - 相对于居中的 html 内容固定的 CSS 重复背景?
我正在尝试在两列上使用 WHERE 子句来加快对大表的查询,MySQL 仅使用 ALERT_ID 列。
有没有办法使用两个索引重写这个查询?
SHOW_INDEX 和 EXPLAIN 输出如下。
show index from alert_hit;
+-----------+------------+-------------------+--------------+-------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-----------+------------+-------------------+--------------+-------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| alert_hit | 0 | PRIMARY | 1 | id | A | 15181402 | NULL | NULL | | BTREE | | |
| alert_hit | 1 | alert_id | 1 | alert_id | A | 20 | NULL | NULL | YES | BTREE | | |
| alert_hit | 1 | timestamp | 1 | timestamp | A | 446511 | NULL | NULL | YES | BTREE | | |
| alert_hit | 1 | data_source_id | 1 | data_source_id | A | 20 | NULL | NULL | YES | BTREE | | |
| alert_hit | 1 | filter_syndicated | 1 | filter_syndicated | A | 20 | NULL | NULL | YES | BTREE | | |
| alert_hit | 1 | unique_id | 1 | unique_id | A | 5060467 | NULL | NULL | YES | BTREE | | |
| alert_hit | 1 | date_created | 1 | date_created | A | 281137 | NULL | NULL | | BTREE | | |
| alert_hit | 1 | language | 1 | language | A | 20 | NULL | NULL | YES | BTREE | | |
| alert_hit | 1 | region | 1 | region | A | 42406 | NULL | NULL | YES | BTREE | | |
| alert_hit | 1 | market_rank | 1 | market_rank | A | 20 | NULL | NULL | YES | BTREE | | |
+-----------+------------+-------------------+--------------+-------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
explain select count(id) as history FROM alert_hit force index(alert_id, timestamp) where alert_id in (9045,9046,9047,9048,9049,9050,9051,9052,9330,9332) AND timestamp between DATE_SUB( NOW(), INTERVAL 1*2 day) and DATE_SUB( NOW(), INTERVAL 1 day);
+----+-------------+-----------+-------+--------------------+----------+---------+------+-------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-----------+-------+--------------------+----------+---------+------+-------+-------------+
| 1 | SIMPLE | alert_hit | range | alert_id,timestamp | alert_id | 5 | NULL | 99578 | Using where |
+----+-------------+-----------+-------+--------------------+----------+---------+------+-------+-------------+
最佳答案
你需要在两个字段上都有一个索引
ALTER TABLE alert_hit ADD INDEX `IDX-alert_id-timestamp` (`alert_id`, `timestamp`);
此外,MySQL 将使用多列索引直到 WHERE 子句中有范围条件的第一个字段,因此在这种情况下顺序很重要,timestamp
应该在索引中排在最后。
正如@spencer7593 建议的那样,选择 COUNT(1)
而不是 count(id)
也可能更好。
关于mysql - 如何在两列上使用 WHERE 子句加速 MySQL 查询?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/11679142/
我是一名优秀的程序员,十分优秀!