我有三个桌子
Student
-------------
id,
matno,
Surname,
faculty_id,
dept_id,
....
Faculty
------------
id,
name,
...
department
-------------------
id,
name,
....
我想使用 matno 选择学生的详细信息,并使用faculty_id和dept_id来选择教师姓名和部门名称。我尝试了所有我能想到的SQL JOIN组合,但只得到一个名称字段。
如果尝试使用其他语句来获取查询,我在第二个查询中也会得到null。
我的SQL查询是
SELECT * FROM student INNER JOIN faculty ON faculty.id = student.faculty_id LEFT JOIN department ON department.id = student.dept_id WHERE student.matno = 1104
答案 0 :(得分:2)
假设faculty_id
和dept_id
是Faculty
和department
表中的外键,此查询应为您提供所需的结果(将???
替换为所需的搜索值matno
):
SELECT s.matno, s.surname, f.name AS faculty, d.name AS department
FROM Student s
JOIN Faculty f ON f.id = s.faculty_id
JOIN department d ON d.id = s.dept_id
WHERE matno = ???
答案 1 :(得分:0)
SELECT * FROM
STUDENT S
LEFT JOIN FACULTY F
ON S.FACULTY_ID = F.ID
LEFT JOIN DEPARTMENT D
ON S.DEPT_ID = D.ID WHERE S.MATNO = "$your_matno";
尝试使用这种左联接,以便至少所有学生都将进入结果集并从中选择必填字段。