class User < ActiveRecord::Base has_many :items end +----+--------+-----+ | id | name | age | +----+--------+-----+ | 1 | user01 | 10 | | 2 | user02 | 20 | | 3 | user03 | 30 | +----+--------+-----+ class Items < ActiveRecord::Base belongs_to :user end +----+---------+----------------------+-----------+ | id | user_id | content | published | +----+---------+----------------------+-----------+ | 1 |
![Railsエンジニアなら最低限これだけは知っておきたいSQLのJOINの動き - Qiita](https://cdn-ak-scissors.b.st-hatena.com/image/square/8439e2f3a72eabf1538df5c13491efaedd9950a6/height=288;version=1;width=512/https%3A%2F%2Fqiita-user-contents.imgix.net%2Fhttps%253A%252F%252Fcdn.qiita.com%252Fassets%252Fpublic%252Farticle-ogp-background-9f5428127621718a910c8b63951390ad.png%3Fixlib%3Drb-4.0.0%26w%3D1200%26mark64%3DaHR0cHM6Ly9xaWl0YS11c2VyLWNvbnRlbnRzLmltZ2l4Lm5ldC9-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%26mark-x%3D142%26mark-y%3D112%26blend64%3DaHR0cHM6Ly9xaWl0YS11c2VyLWNvbnRlbnRzLmltZ2l4Lm5ldC9-dGV4dD9peGxpYj1yYi00LjAuMCZ3PTYxNiZ0eHQ9JTQwdmlwdGFrZWNoYW4mdHh0LWNvbG9yPSUyMzIxMjEyMSZ0eHQtZm9udD1IaXJhZ2lubyUyMFNhbnMlMjBXNiZ0eHQtc2l6ZT0zNiZ0eHQtYWxpZ249bGVmdCUyQ3RvcCZzPWY2YzU3NWU4NTM2ZWIzNjk5NmFkZTA5OGZiODEyYzhk%26blend-x%3D142%26blend-y%3D491%26blend-mode%3Dnormal%26s%3D1c3c27139b31cb5a2ee81db6000769c2)