创建一个包含 3 个表的 sql 视图

Question

I currently have three tables Engineer, Classes, and Faculty. I am trying to create a view that will display Engineer firstname and lastname, Classes subject and title, and Faculty lastname and email. All under one view I've tried multiple different ways but still can't figure out how to properly execute

CREATE VIEW RETRIEVAL
SELECT a.firstname, a.lastname, b.flastname, b.email, c.subject, c.title
FROM engineer a 
INNER JOIN faculty b ON a.lastname = b.flastname
INNER JOIN classes c on c.cid = b.fid;

Answer 1

[Edited after clarifications were provided by the asker]

It looks like you want to do something along the lines of:

SELECT e.firstname, e.lastname, e.email, f.lastname, c.subject, c.title
FROM engineer e 
   INNER JOIN faculty f ON e.faculty_id = f.id
   INNER JOIN classes c on f.id = c.faculty_id
WHERE c.subject > c.title

This is if you have an id field in faculty and a faculty_id field in classes. Also a faculty_id in engineer

However I'm not sure I understand what do you want to achieve with the c.subject > c.title condition as it is not mentioned in the question.

This would work for a many-to-one relationship between engineer and faculty .

If there's a many-to-many relationship between engineer and faculty then you need an additional table engineer_faculty where you store the relationships between the two and update the query accordingly

Before committing to create the VIEW , run the SELECT by itself and see if it shows the results that you want. If it does, then create the view.

Try providing some example data on https://www.mycompiler.io/new/sql We could then be of better help.

Answer 2

You should use the aliases you gave to the tables in the FROM cluase as you did in the WHERE clause:

CREATE VIEW RETRIEVAL AS 
SELECT a.firstname, a.lastname, b.lastname, b.email, c.subject, c.title
FROM engineer a, faculty b, classes c
WHERE a.lastname = b.lastname 
      AND c.subject > c.title;