在Postgresql中连接多个表

Question

I'm practising for an upcoming database exam and I'm trying to get my head around nested and multiple joins in SQL, specifically the Postgresql syntax. I want to return all the student names and department names of all students that achieved grade A.

Here's my schema.

CREATE TABLE student1 (
    student_number INTEGER NOT NULL PRIMARY KEY,
    name TEXT NOT NULL,
    class INTEGER NOT NULL,
    major TEXT NOT NULL
);


CREATE TABLE course1 (
    course_name TEXT NOT NULL,
    course_number TEXT NOT NULL PRIMARY KEY,
    credit_hours INTEGER NOT NULL,
    department TEXT NOT NULL
);

CREATE TABLE section1 (
    section_identifer INTEGER NOT NULL PRIMARY KEY,
    course_number TEXT NOT NULL,
    semester TEXT NOT NULL,
    year INTEGER NOT NULL,
    instructor TEXT NOT NULL,
    FOREIGN KEY (course_number) REFERENCES course1(course_number) ON DELETE CASCADE
);

CREATE TABLE grade_report1 (
    id SERIAL NOT NULL PRIMARY KEY,
    student_number INTEGER NOT NULL,
    section_identifer INTEGER NOT NULL,
    grade TEXT NOT NULL,
    FOREIGN KEY (student_number) REFERENCES student1(student_number) ON DELETE CASCADE,
    FOREIGN KEY (section_identifer) REFERENCES section1(section_identifer) ON DELETE CASCADE
);

I put together a nested statement that I thought would work:

SELECT t1.name, t3.department
FROM (student1 t1 INNER JOIN grade_report1 t2 ON t1.student_number = t2.student_number) t5
INNER JOIN (course1 t3 INNER JOIN section1 t4 ON t3.course_number = t4.course_number) t6
ON t5.section_identifer = t6.section_identifer
WHERE t2.grade = 'A';

However, this gives me the error invalid reference to FROM-clause entry for table "t1" . I'm guessing it is because that is not how you are supposed to name/reference JOINS. I would like a way to JOIN all of these tables together. Thanks!

Answer 1

Remove the parentheses and fix the aliases:

SELECT s.name, c.department
FROM student1 s INNER JOIN
     grade_report1 gr
     ON gr.student_number = s.student_number INNER JOIN
     section1 sec
     ON sec.section_identifer = gr.section_identifer INNER JOIN
     course1 c 
     ON sec.course_number = c.course_number
WHERE gr.grade = 'A';

The parentheses are allowed, but they are not needed. When using parentheses (which is very, very rarely needed), they do not get separate aliases.