也许你可以建议应该采用什么方法？目标是通过表中的post_索引列对公司进行排序。 mysql> EXPLAIN SELECT * FROM companies INNER JOIN post_indices ON post_indices.id =

也许你可以建议应该采用什么方法？目标是通过表中的

post_索引

列对

公司

进行排序。

mysql> EXPLAIN SELECT * FROM companies INNER JOIN post_indices ON post_indices.id = companies.post_index_id WHERE companies.deleted_at IS NULL ORDER BY post_indices.id LIMIT 1;
+----+-------------+--------------+------------+--------+----------------------------------------------------------------------------------------------------------------+-------------------------------+---------+------------------------------------------------------+--------+----------+---------------------------------------------------------------------+
| id | select_type | table        | partitions | type   | possible_keys                                                                                                  | key                           | key_len | ref                                                  | rows   | filtered | Extra                                                               |
+----+-------------+--------------+------------+--------+----------------------------------------------------------------------------------------------------------------+-------------------------------+---------+------------------------------------------------------+--------+----------+---------------------------------------------------------------------+
|  1 | SIMPLE      | companies    | NULL       | ref    | index_companies_on_post_index_id,index_companies_on_deleted_at,index_companies_on_deleted_at_and_post_index_id | index_companies_on_deleted_at | 6       | const                                                | 638692 |   100.00 | Using index condition; Using where; Using temporary; Using filesort |
|  1 | SIMPLE      | post_indices | NULL       | eq_ref | PRIMARY                                                                                                        | PRIMARY                       | 4       | enbro_purecrm_eu_development.companies.post_index_id |      1 |   100.00 | NULL                                                                |
+----+-------------+--------------+------------+--------+----------------------------------------------------------------------------------------------------------------+-------------------------------+---------+------------------------------------------------------+--------+----------+---------------------------------------------------------------------+
2 rows in set, 1 warning (0.00 sec)


mysql> EXPLAIN SELECT * FROM companies USE INDEX(index_companies_on_post_index_id) INNER JOIN post_indices ON post_indices.id = companies.post_index_id WHERE companies.deleted_at IS NULL ORDER BY post_indices.id LIMIT 1;
+----+-------------+--------------+------------+--------+----------------------------------+---------+---------+------------------------------------------------------+---------+----------+----------------------------------------------+
| id | select_type | table        | partitions | type   | possible_keys                    | key     | key_len | ref                                                  | rows    | filtered | Extra                                        |
+----+-------------+--------------+------------+--------+----------------------------------+---------+---------+------------------------------------------------------+---------+----------+----------------------------------------------+
|  1 | SIMPLE      | companies    | NULL       | ALL    | index_companies_on_post_index_id | NULL    | NULL    | NULL                                                 | 1277385 |    10.00 | Using where; Using temporary; Using filesort |
|  1 | SIMPLE      | post_indices | NULL       | eq_ref | PRIMARY                          | PRIMARY | 4       | enbro_purecrm_eu_development.companies.post_index_id |       1 |   100.00 | NULL                                         |
+----+-------------+--------------+------------+--------+----------------------------------+---------+---------+------------------------------------------------------+---------+----------+----------------------------------------------+
2 rows in set, 1 warning (0.00 sec)


mysql> EXPLAIN SELECT * FROM companies USE INDEX(index_companies_on_deleted_at_and_post_index_id) INNER JOIN post_indices ON post_indices.id = companies.post_index_id WHERE companies.deleted_at IS NULL ORDER BY post_indices.id LIMIT 1;
+----+-------------+--------------+------------+--------+-------------------------------------------------+-------------------------------------------------+---------+------------------------------------------------------+--------+----------+--------------------------------------------------------+
| id | select_type | table        | partitions | type   | possible_keys                                   | key                                             | key_len | ref                                                  | rows   | filtered | Extra                                                  |
+----+-------------+--------------+------------+--------+-------------------------------------------------+-------------------------------------------------+---------+------------------------------------------------------+--------+----------+--------------------------------------------------------+
|  1 | SIMPLE      | companies    | NULL       | ref    | index_companies_on_deleted_at_and_post_index_id | index_companies_on_deleted_at_and_post_index_id | 6       | const                                                | 638692 |   100.00 | Using index condition; Using temporary; Using filesort |
|  1 | SIMPLE      | post_indices | NULL       | eq_ref | PRIMARY                                         | PRIMARY                                         | 4       | enbro_purecrm_eu_development.companies.post_index_id |      1 |   100.00 | NULL                                                   |
+----+-------------+--------------+------------+--------+-------------------------------------------------+-------------------------------------------------+---------+------------------------------------------------------+--------+----------+--------------------------------------------------------+
2 rows in set, 1 warning (0.00 sec)

| companies | CREATE TABLE `companies` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
`address` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
`post_index_id` int(11) DEFAULT NULL,
`vat` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
`note` text COLLATE utf8_unicode_ci,
`state` varchar(255) COLLATE utf8_unicode_ci NOT NULL DEFAULT 'new',
`deleted_at` datetime DEFAULT NULL,
`lead_list_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `index_companies_on_vat` (`vat`),
KEY `index_companies_on_post_index_id` (`post_index_id`),
KEY `index_companies_on_state` (`state`),
KEY `index_companies_on_deleted_at` (`deleted_at`),
KEY `index_companies_on_deleted_at_and_post_index_id` (`deleted_at`,`post_index_id`),
KEY `index_companies_on_lead_list_id` (`lead_list_id`),
CONSTRAINT `fk_rails_5fc7f5c6b9` FOREIGN KEY (`lead_list_id`) REFERENCES `lead_lists` (`id`),
CONSTRAINT `fk_rails_79719355c6` FOREIGN KEY (`post_index_id`) REFERENCES `post_indices` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2523518 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci |

| post_indices | CREATE TABLE `post_indices` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`county` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
`postal_code` int(11) DEFAULT NULL,
`group_part` int(11) DEFAULT NULL,
`group_number` int(11) DEFAULT NULL,
`group_name` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
`city` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
`created_at` datetime NOT NULL,
`updated_at` datetime NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3101 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci |

mysql> explain SELECT * FROM companies      INNER JOIN post_indices         ON companies.post_index_id = post_indices.id     WHERE companies.deleted_at is NULL     ORDER BY post_indices.id     LIMIT 1;
+----+-------------+--------------+-------+----------------------------------------------------------------------------------------------------------------+-------------------------------------------------+---------+----------------------------------------------------+------+-----------------------+
| id | select_type | table        | type  | possible_keys                                                                                                  | key                                             | key_len | ref                                                | rows | Extra                 |
+----+-------------+--------------+-------+----------------------------------------------------------------------------------------------------------------+-------------------------------------------------+---------+----------------------------------------------------+------+-----------------------+
|  1 | SIMPLE      | post_indices | index | PRIMARY                                                                                                        | PRIMARY                                         | 4       | NULL                                               |    1 | NULL                  |
|  1 | SIMPLE      | companies    | ref   | index_companies_on_post_index_id,index_companies_on_deleted_at,index_companies_on_deleted_at_and_post_index_id | index_companies_on_deleted_at_and_post_index_id | 11      | const,enbro_purecrm_eu_development.post_indices.id |  283 | Using index condition |
+----+-------------+--------------+-------+----------------------------------------------------------------------------------------------------------------+-------------------------------------------------+---------+----------------------------------------------------+------+-----------------------+
2 rows in set (0,00 sec)

SELECT * FROM companies AS c
INNER JOIN post_indices AS pi
    ON c.post_index_id = pi.id
WHERE    c.deleted_at is NULL
ORDER BY c.post_index_id           -- Note
LIMIT 1;

INDEX(deleted_at, post_index_id)  -- note

SELECT * FROM post_indices 
    STRAIGHT_JOIN companies FORCE INDEX(index_companies_on_deleted_at_and_post_index_id)
        ON companies.post_index_id = post_indices.id
    WHERE companies.deleted_at is NULL
    ORDER BY post_indices.id
    LIMIT 1;