[英]MySql Join Query left join
我有表格名稱的學生,其字段為student_id,house_id等。以及主題,房屋,students_subjects
我正在使用此查詢
SELECT students_subjects.student_id,students.house_id,students_subjects.subject_id,subjects.subject_name,students.rollno,students.first_name, students.last_name FROM
students_subjects LEFT JOIN students on students_subjects.student_id=students.id
LEFT JOIN subjects on students_subjects.subject_id=subjects.id WHERE students_subjects.class_years_section_id=1
這對我來說很好。
現在我也想從房屋表中獲得房屋名稱
我試過這個查詢
SELECT students_subjects.student_id,students.house_id,houses.house_name, students_subjects.subject_id,subjects.subject_name,students.rollno,students.first_name, students.last_name FROM
students_subjects LEFT JOIN students on students_subjects.student_id=students.id
LEFT JOIN subjects on students_subjects.subject_id=subjects.id
LEFT JOIN在students.house_id = houses.id上的房屋WHERE students_subjects.class_years_section_id = 1
AND students_subjects.school_session_id=1 AND students.is_active=1
它給了我house_name = NULL
有人能告訴我如何獲得房屋名稱嗎? 使用聯接查詢
謝謝
您的查詢錯誤是由WHERE
子句后面的LEFT JOIN
關鍵字引起的,
SELECT students_subjects.student_id,
students.house_id,
students_subjects.subject_id,
subjects.subject_name,
students.rollno,
students.first_name,
students.last_name
FROM students_subjects
LEFT JOIN students
on students_subjects.student_id=students.id
LEFT JOIN subjects
on students_subjects.subject_id=subjects.id
LEFT JOIN houses
on students.house_id=houses.id
WHERE students_subjects.class_years_section_id = 1 AND
students_subjects.school_session_id = 1 AND
students.is_active = 1
請記住, JOIN
是FROM
子句的一部分。
更新1
SELECT b.student_id,
a.house_id,
b.subject_id,
c.subject_name,
a.rollno,
a.first_name,
a.last_name,
d.house_name
FROM students a
INNER JOIN students_subjects b
ON b.student_id = a.id
INNER JOIN subjects c
ON b.subject_id = c.id
INNER JOIN houses d
ON a.house_id = d.id
WHERE b.class_years_section_id = 1 AND
b.school_session_id = 1 AND
a.is_active = 1
您已經錯過了放置WHERE
子句的方法,請嘗試以下操作:
SELECT students_subjects.student_id,students.house_id,students_subjects.subject_id,subjects.subject_name,students.rollno,students.first_name, students.last_name
FROM students_subjects
LEFT JOIN students ON students_subjects.student_id=students.id
LEFT JOIN subjects ON students_subjects.subject_id=subjects.id
LEFT JOIN houses ON students.house_id=houses.id
WHERE students_subjects.class_years_section_id=1
AND students_subjects.school_session_id=1 AND students.is_active=1
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