使用帶有外鍵的MySQL連接三個表

Question

現在我有一個下面的查詢只運行兩個表！ 但是，我想使用帶有外鍵的MySQL加入三個表！ 我將SQL代碼粘貼在下面以查看外鍵！

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

這是我的數據庫：

--
-- 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

您正在聯接3個表，但沒有聯接正確的外鍵。

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

演示