mysql - 使用 MySQL 外键连接三个表

Question

现在我有一个以下查询仅运行两个表!但是，我想使用 MySQL 和外键连接三个表!我将 SQL 代码粘贴到下面来查看外键!

$sql  = "SELECT student.*, courses.* 
        FROM student 
        INNER JOIN courses ON student.id=courses.id_courses  
        INNER JOIN schedule ON schedule.id_schedule = schedule.id";

这是我的数据库:

--
-- Table structure for table `courses`
--


--
-- Constraints for table `schedule`
--
ALTER TABLE `schedule`
  ADD CONSTRAINT `schedule_ibfk_1` FOREIGN KEY (`id_courses`) REFERENCES `courses` (`id_courses`) ON DELETE CASCADE ON UPDATE CASCADE,
  ADD CONSTRAINT `schedule_ibfk_2` FOREIGN KEY (`id`) REFERENCES `student` (`id`) ON DELETE CASCADE ON UPDATE CASCADE;

Answer 1

您正在联接 3 个表，但未联接正确的外键。

SELECT student.*, courses.*
FROM schedule
JOIN student ON student.id = schedule.id
JOIN courses ON courses.id_courses = schedule.id_courses

DEMO