如何让mysql派生表使用索引

Question

MySQL 版本 5.6.33

我有两个表（files & details）要进行内部连接

表files，有一个名为idx_record(record_id)

的索引

表details，有一个名为idx_end_org_record的索引（end_at, org_id, record_id）

explain
SELECT
    id as file_id,
    record_id,
    recording_path
FROM `files`
INNER JOIN
(
    SELECT `details`.`record_id`
    FROM `details` 
    WHERE `details`.`org_id` IN (6231, 6232, 6233, 6234) 
    AND (`details`.`end_at` BETWEEN '2017-05-31 16:00:00' AND '2017-06-13 16:00:00') 
    ORDER BY end_at desc
) as b
    on `files`.record_id = b.record_id 
WHERE (file_name IS NOT NULL )
LIMIT 30

输出如下

+----+-------------+--------------+-------+--------------------+--------------------+---------+------------------+---------+--------------------------+
| id | select_type | table        | type  | possible_keys      | key                | key_len | ref              | rows    | Extra                    |
+----+-------------+--------------+-------+--------------------+--------------------+---------+------------------+---------+--------------------------+
|  1 | PRIMARY     | <derived2>   | ALL   | NULL               | NULL               | NULL    | NULL             | 3844632 | Using where              |
|  1 | PRIMARY     | files        | ref   | idx_record         | idx_record         | 5       | b.record_id      |       1 | Using where              |
|  2 | DERIVED     | details      | range | idx_end_org_record | idx_end_org_record | 11      | NULL             | 3844632 | Using where; Using index |
+----+-------------+--------------+-------+--------------------+--------------------+---------+------------------+---------+--------------------------+

如您所见，<derived2> 表没有使用任何索引，这使得该查询需要将近 1 秒才能完成。

感谢任何帮助！

---

此外，在查询中删除 WHERE (file_name IS NOT NULL ) 没有任何区别。

而在 mysql 5.7 中，这个问题甚至不存在，但目前我正在尝试在 5.6 中解决这个问题。

Answer 1

我没有看到子查询的意义。特别是，子查询中的ORDER BY 毫无意义。如果您将查询编写为两个表之间的直接连接，那么优化器应该能够利用连接列上的索引：

SELECT
id as file_id,
record_id,
recording_path
FROM files f
INNER JOIN details d
    ON f.record_id = d.record_id AND
       d.org_id IN (6231, 6232, 6233, 6234) AND
       d.end_at BETWEEN '2017-05-31 16:00:00' AND '2017-06-13 16:00:00'
WHERE f.file_name IS NOT NULL
ORDER BY <some column>    -- it doesn't make sense most of the time to use LIMIT
LIMIT 30                  -- without ORDER BY

在details 表中的record_id、org_id 和end_at 以及files 表中的file_name 上添加索引，应该会给您带来一些性能改进。