关系代数

Question

你能帮我解决这个关系代数吗？我得到了这个DB (论文答辩)；

• Teachers(Teacher_ID，名称，Specialty)
• Projects(Project_ID，标题，Specialty)
• Thesis(Thesis_ID，Project_ID，Jury_ID，Decision)
• Juries(Jury_ID，Supervisor_ID，First_Member_ID，Second_Member_ID)

我想要找到代数查询，以获得教师(ID，名字)监督论文在他们的专业；

我已经在SQL中这样做了，它应该是这样的：

Select Teacher_ID, Name  
From Teachers T  
Where Teacher_ID IN
      (Select Supervisor_ID  
       From Juries  
       Where Jury_ID IN
             (Select Jury_ID  
              From Thesis  
              Where Project_ID IN 
                    (Select Project_ID  
                     From Projects P  
                     Where T.Specialty = P.Specialty)))  

谢谢你的帮忙!

Answer 1

你想这么做吗？

select Te.Teacher_ID,Te.Name from thesis t
join project P on (T.Speciality =P.Speciality)
join Juries J on ( J.jury_ID = T.Jury_id)
join Teacher Te on (Te.Teacher_ID = J.Supervisor_ID)

Answer 2

我想我已经找到了答案，多亏了Mulki的帮助：

R1 <- Thesis ⋈ (Project_ID) Projects
R2 <- Teachers ⋈ (Teacher_ID=Supervisor_ID) Juries
R3 <- π Teacher_ID, Name (R2 ⋈ (Specialty ^ Jury_ID) R1)

因此，首先在R1中，我们得到了论文的具体内容(这是Mulki的回答有帮助的地方)

然后，在R2中，我们得到了作为监督员的教师

最后，我们加入了R2和R1，条件是它们具有相同的Jury_ID和特性

并只显示它们的ID和名称。