Question

任何帮助将不胜感激。

我有两张桌子：

CREATE TABLE `users` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `username` varchar(255) NOT NULL,
  `username_canonical` varchar(255) NOT NULL,
  `email` varchar(255) NOT NULL,
  `email_canonical` varchar(255) NOT NULL,
  `enabled` tinyint(1) NOT NULL,
  `salt` varchar(255) NOT NULL,
  `password` varchar(255) NOT NULL,
  `last_login` datetime DEFAULT NULL,
  `locked` tinyint(1) NOT NULL,
  `expired` tinyint(1) NOT NULL,
  `expires_at` datetime DEFAULT NULL,
  `confirmation_token` varchar(255) DEFAULT NULL,
  `password_requested_at` datetime DEFAULT NULL,
  `roles` longtext NOT NULL COMMENT '(DC2Type:array)',
  `credentials_expired` tinyint(1) NOT NULL,
  `credentials_expire_at` datetime DEFAULT NULL,
  `messages_unread_count` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `UNIQ_1483A5E992FC23A8` (`username_canonical`),
  UNIQUE KEY `UNIQ_1483A5E9A0D96FBF` (`email_canonical`)
  ) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8

和

CREATE TABLE `blog_posts` (
 `id` bigint(20) NOT NULL AUTO_INCREMENT,
 `user_id` bigint(20) DEFAULT NULL,
 `category_id` int(11) DEFAULT NULL,
 `title` varchar(255) NOT NULL,
 `content` longtext NOT NULL,
 `tags` varchar(512) NOT NULL,
 `timestamp_created` datetime NOT NULL,
 `timestamp_updated` datetime NOT NULL,
 `is_visible` tinyint(1) NOT NULL,
 `is_deleted` tinyint(1) NOT NULL,
 PRIMARY KEY (`id`),
 KEY `IDX_78B2F93212469DE2` (`category_id`),
 KEY `IDX_78B2F932A76ED395` (`user_id`),
 CONSTRAINT `FK_78B2F932A76ED395` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`),
 CONSTRAINT `FK_78B2F93212469DE2` FOREIGN KEY (`category_id`) REFERENCES `blog_categories`     (`id`)
 ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8

我希望选择所有帖子限制输出的帖子作者，给我一个建议 - 我怎么能强制查询使用索引：

select p.*, u.* from blog_posts p join users u on p.user_id = u.id limit 0,10;

解释输出：

+----+-------------+-------+------+----------------------+----------------------+---------+----------+------+-------------+
| id | select_type | table | type | possible_keys        | key                  | key_len | ref      | rows | Extra       |
+----+-------------+-------+------+----------------------+----------------------+---------+----------+------+-------------+
|  1 | SIMPLE      | u     | ALL  | PRIMARY              | NULL                 | NULL    | NULL     |    1 |             |
|  1 | SIMPLE      | p     | ref  | IDX_78B2F932A76ED395 | IDX_78B2F932A76ED395 | 9       | sky.u.id |    1 | Using where |
+----+-------------+-------+------+----------------------+----------------------+---------+----------+------+-------------+

加入用户表时有没有办法使用索引？

Answer 1

如果您在blogposts.userid和users.id之间设置FK关系，Mysql将自动使用索引。

所以创建FK关系：

CONSTRAINT blogposts_userid FOREIGN KEY (user_id) REFERENCES users (id)

MySQL在连接两个表时使用索引

1 个答案: