导入
表的 INNER JOIN
学习如何在 SQL 中连接多个表。
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1SELECT e.first_name, 2 e.last_name, 3 d.department_name 4FROM employees AS e 5INNER JOIN departments AS d 6ON e.department_id = d.department_id;
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1SELECT e.first_name, 2 e.last_name, 3 e.salary, 4 d.department_name 5FROM employees AS e 6INNER JOIN departments AS d 7ON e.department_id = d.department_id;
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1SELECT e.first_name, 2 e.last_name, 3 d.department_name 4FROM employees AS e 5INNER JOIN departments AS d 6ON e.department_id = d.department_id;
表
| 概念 | 作用 | 示例 |
|---|---|---|
| INNER JOIN | 合并两张表之间匹配的行 | employees INNER JOIN departments |
| ON | 定义两表的连接条件 | ON e.department_id = d.department_id |
| 表别名 | 便于阅读的简短别名 | employees AS e |
| 结果 | 只出现匹配的记录 | 拥有有效 department_id 的员工 |