使用MySQL加入三个表

Question

我有三个名为的表

**Student Table**
-------------
id    name
-------------
1     ali
2     ahmed
3     john
4     king

**Course Table**
-------------
id    name
-------------
1     physic
2     maths
3     computer
4     chemistry

**Bridge**
-------------
sid    cid
-------------
1     1
1     2
1     3
1     4
2     1
2     2
3     3
3     4
4     1
4     2

现在用他研究过的课程名称来显示学生姓名,

**Result**
---------------------------
Student        Course
---------------------------
ahmed         physic
ahmed         maths
ahmed         computer
ahmed         chemistry
ali           physic
ali           maths
john          computer
john          chemistry
king          physic
king          maths

我构建以下查询

select s.name as Student, c.name as Course from student s, course c join bridge b on c.id = b.cid order by s.name

但它没有返回所需的结果......

如果我想找到谁是其他经理,那么规范化形式会是什么:

**employee**
-------------------
id        name
-------------------
1         ali
2         king
3         mak
4         sam
5         jon

**manage**
--------------
mid      eid
--------------
1         2
1         3
3         4
4         5

并希望得到这个结果:

**result**
--------------------
Manager      Staff
--------------------
ali          king
ali          mak
mak          sam
sam          jon

Answer 1

使用ANSI语法,如何加入表格将更加清晰:

SELECT s.name as Student, c.name as Course 
FROM student s
    INNER JOIN bridge b ON s.id = b.sid
    INNER JOIN course c ON b.cid  = c.id 
ORDER BY s.name 

Answer 2

只需使用:

select s.name "Student", c.name "Course"
from student s, bridge b, course c
where b.sid = s.sid and b.cid = c.cid 

Answer 3

用于规范化表格

select e1.name as 'Manager', e2.name as 'Staff'
from employee e1 
left join manage m on m.mid = e1.id
left join employee e2 on m.eid = e2.id

Answer 4

SELECT *
FROM user u
JOIN user_clockits uc ON u.user_id=uc.user_id
JOIN clockits cl ON cl.clockits_id=uc.clockits_id
WHERE user_id = 158