SQL内连接在三个表上

Question

我有三张桌子需要检查才能找出教授活跃的课程。

1. table_teacher
2. table_course;和
3. table_teacher_holds_course

table_teacher看起来像这样：

username | title
---------+----------
john     | professor
mark     | assistant

table_course看起来像这样：

 course_code | course_name | semester | school_year
-------------+-------------+----------+------------
 course_code1| course1     |semester1 | 2015
 course_code2| course2     |semester2 | 2015
 course_code3| course3     |semester3 | 2015

table_teacher_holds_course看起来像这样：

username | course_code
---------+-------------
 john    |course_code1
 mark    |course_code2

当我在登录页面时拥有教授用户名时，我想在这三张桌子上做左内连接，以便从table_course中显示教授课程

有人可以帮我这个，因为我第一次使用sql在几个表中加入搜索。

Answer 1

加入表格公共字段

SELECT * 
FROM table_teacher t
INNER JOIN table_teacher_holds_course hc ON t.username = hc.username
INNER JOIN table_course c ON hc.course_code = c.course_code

相关示例：

SELECT t.title, t.username, c.course_code, c.course_name, c.semester, c.school_year 
FROM table_teacher t
INNER JOIN table_teacher_holds_course hc ON t.username = hc.username
INNER JOIN table_course c ON hc.course_code = c.course_code
WHERE t.username = 'John'

结果：

title      username course_code  course_name semester  school_year 
professor  John     course_code1 course1     semester1 2015