找和室友一样的薪水

Question

有三个表。 学生，室友，工资。列如下

student
student_id (Primary Key) | smallint
student_name             | varchar(30)

roommate
student_id (Primary Key) | smallint
roommate_id              | smallint

salary
student_id (Primary Key) | smallint
salary                   | float(10,2)

现在我需要打印学生的姓名和他们的室友相同。 好吧，我能够找到薪水相同的人。但是我找不到他们是否是室友。该怎么做？

Answer 1

以下是对MySQL有帮助的查询

    def doStuff():
        global selected
        selected = lb.curselection()
        if selected: # only perform  if user made a selection
            for index in selected:
                selection = (lb.get(index))# how you get the value of the selection from a listbox
    print(selection)
    ```

希望这会有所帮助

Answer 2

SELECT st.student_name FROM student st /* st - Student */
JOIN roommate rm ON (rm.student_id = st.student_id) /* rm - Student roommate */ 
JOIN salary st_salary ON (st.student_id = st_salary.student_id) /* st_salary - student's salary */ 
JOIN salary rm_salary ON /* (rm.roommate_id = rm_salary.student_id) /* rm_salary - student'ts roomate salary */ 
WHERE st_salary.salary = rm_salary.salary;