爲什麼我的SELECT語句顯示重複記錄？

Question

我在克服這個錯誤方面遇到了一些麻煩。當我完整地執行SELECT語句時，會顯示一條重複的消息。

的代碼是：

SELECT students.first_name, last_name ,entries.subject_id, subject_name, level_of_entry 
FROM students, subjects , entries 
WHERE subjects.subject_id=entries.subject_id 
AND students.student_id=entries.student_id 
AND exam_board='ocr'; 

This is what happens after that code is processed

These are the tables which the data is coming from

有沒有辦法停止複製或刪除重複的行嗎？

複製的行是第6和第7行;一個與Zeynnata Rein。

感謝您的幫助！

PS：對不起，物理學

Answer 1

拼寫錯誤，你必須通過student_id數據

Answer 2

使用組，因爲你不加入它返回所有匹配組合的表。儘量明確連接：

SELECT st.first_name, st.last_name, e.subject_id, su.subject_name, su.level_of_entry 
FROM students st 
LEFT JOIN entries e 
ON st.student_id = e.student_id 
LEFT JOIN subjects su 
ON e.subject_id = su.subject_id 
WHERE su.exam_board = 'ocr';