Mysql 關鍵字JOIN，LEFT JOIN，RIGHT JOIN

數據庫多表關聯查詢
student表

class表

1. JOIN等同於INNER JOIN,即內連接，不滿足ON條件的會直接過濾掉，不顯示
SELECT * FROM student s JOIN class c ON s.class_id = c.id

2. LEFT JOIN等同於LEFT OUTER JOIN，左外連接，不滿足ON條件的會保留左邊那張表的數據，右邊表數據直接顯示NULL
SELECT * FROM student s LEFT JOIN class c ON s.class_id = c.id

3. RIGHT JOIN等同於RIGHT OUTER JOIN，右外連接，不滿足ON條件的會保留右邊那張表的數據，左邊表數據直接顯示NULL
SELECT * FROM student s RIGHT JOIN class c ON s.class_id = c.id