平均等級点の平均を扱うクエリ

Question

このSQL文を正常に動作させるために問題が発生しました。このように計算されたギャップが想定されています。メジャーGPAは、GPAと同じ方法で計算されますが、メジャーからのコースのみが計算に含まれます。たとえば、CSの学生がCSクラスにAを、MathクラスにBを取得したとすると、その学生の主要なGPAは4.0になります。

学生とその主要GPAをリストします。結果には、専攻科目を履修していない生徒を含める必要はありません。

これまでのところ、私が望むものを完全に返さない以下のクエリがあります。

select sum(value*units)/sum(units) as GPA ,f.name from faculty f 
inner join sections s on s.instructor_id = f.id 
inner join courses c on c.id=s.id 
inner join grades g on g.value =c.units 
group by f.name 

私が手の表は、私が欲しいものはほとんどですが、それもどんな授業をしていない学生のためGPASを示し

name gpa 
Art  4.00 
Bob  4.00 
Pat  3.30 
Amy  3.30 
Kim  3.30 
Sue  3.30 
Joe  2.70 
Lee  2.70 
Max 2.70 

です。

データベースが

create table departments (
    id  integer primary key, 
    name varchar(255) 
); 

insert into departments (id, name) values (10, 'Computer Science'); 
insert into departments (id, name) values (20, 'Math'); 
insert into departments (id, name) values (30, 'Drama'); 

create table students (
    id    integer primary key, 
    name   varchar(255), 
    graduation_date date, 
    major_id  integer references departments(id) 
); 

insert into students (id, name, graduation_date, major_id) values 
    (1, 'Joe', null, 10); 
insert into students (id, name, graduation_date, major_id) values 
    (2, 'Amy', '2009-04-22', 20); 
insert into students (id, name, graduation_date, major_id) values 
    (3, 'Max', null, 10); 
insert into students (id, name, graduation_date, major_id) values 
    (4, 'Sue', '2009-01-10', 20); 
insert into students (id, name, graduation_date, major_id) values 
    (5, 'Bob', '2009-03-05', 30); 
insert into students (id, name, graduation_date, major_id) values 
    (6, 'Kim', null, 20); 
insert into students (id, name, graduation_date, major_id) values 
    (7, 'Art', null, 30); 
insert into students (id, name, graduation_date, major_id) values 
    (8, 'Pat', '2005-07-11', 20); 
insert into students (id, name, graduation_date, major_id) values 
    (9, 'Lee', null, 10); 

create table grades (
    id   integer primary key, 
    letter  varchar(255) not null unique, 
    value  real 
); 

insert into grades (id, letter, value) values (1, 'A', 4.0); 
insert into grades (id, letter, value) values (2, 'A-', 3.7); 
insert into grades (id, letter, value) values (3, 'B+', 3.3); 
insert into grades (id, letter, value) values (4, 'B', 3.0); 
insert into grades (id, letter, value) values (5, 'B-', 2.7); 
insert into grades (id, letter, value) values (6, 'C+', 2.3); 
insert into grades (id, letter, value) values (7, 'C', 2.0); 
insert into grades (id, letter, value) values (8, 'C-', 1.7); 
insert into grades (id, letter, value) values (9, 'D+', 1.3); 
insert into grades (id, letter, value) values (10, 'D', 1.0); 
insert into grades (id, letter, value) values (11, 'D-', 0.7); 
insert into grades (id, letter, value) values (12, 'F', 0.0); 
insert into grades (id, letter) values (13, 'CR'); 
insert into grades (id, letter) values (14, 'NC'); 

create table courses (
    id    integer primary key, 
    title   varchar(255), 
    units   integer, 
    department_id integer references departments(id) 
); 

insert into courses (id, title, units, department_id) values 
    (12, 'Databases', 4, 10); 
insert into courses (id, title, units, department_id) values 
    (22, 'Compilers', 4, 10); 
insert into courses (id, title, units, department_id) values 
    (32, 'Calculus 1', 4, 20); 
insert into courses (id, title, units, department_id) values 
    (42, 'Algebra', 4, 20); 
insert into courses (id, title, units, department_id) values 
    (52, 'Acting', 4, 30); 
insert into courses (id, title, units, department_id) values 
    (62, 'Elocution', 2, 30); 
insert into courses (id, title, units, department_id) values 
    (72, 'Calculus 2', 4, 20); 
insert into courses (id, title, units, department_id) values 
    (82, 'Topology', 4, 20); 

create table sections (
    id    integer primary key, 
    course_id  integer not null references courses(id), 
    instructor_id integer references faculty(id), 
    year   integer 
); 

insert into sections (id, course_id, instructor_id, year) values 
    (12, 12, 6, 2007); 
insert into sections (id, course_id, instructor_id, year) values 
    (13, 12, 1, 2008); 
insert into sections (id, course_id, instructor_id, year) values 
    (14, 22, 1, 2008); 
insert into sections (id, course_id, instructor_id, year) values 
    (23, 12, 6, 2009); 
insert into sections (id, course_id, instructor_id, year) values 
    (24, 22, 1, 2009); 
insert into sections (id, course_id, instructor_id, year) values 
    (32, 32, 2, 2008); 
insert into sections (id, course_id, instructor_id, year) values 
    (33, 32, 2, 2009); 
insert into sections (id, course_id, instructor_id, year) values 
    (34, 82, 2, 2009); 
insert into sections (id, course_id, instructor_id, year) values 
    (43, 32, 3, 2008); 
insert into sections (id, course_id, instructor_id, year) values 
    (51, 62, 4, 2008); 
insert into sections (id, course_id, instructor_id, year) values 
    (52, 52, 4, 2008); 
insert into sections (id, course_id, instructor_id, year) values 
    (53, 62, 4, 2009); 
insert into sections (id, course_id, instructor_id, year) values 
    (54, 52, 4, 2009); 

create table enrollment (
    id   integer primary key, 
    student_id integer not null references students(id), 
    section_id integer not null references sections(id), 
    grade_id integer references grades(id) 
); 

insert into enrollment (id, student_id, section_id, grade_id) values 
    (14, 1, 12, 8); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (15, 1, 13, 3); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (16, 1, 14, 5); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (17, 1, 32, 1); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (18, 1, 34, 2); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (19, 1, 53, 13); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (24, 3, 12, 2); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (25, 3, 14, 5); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (26, 3, 32, 1); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (27, 3, 34, 2); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (28, 3, 54, 7); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (34, 2, 43, 3); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (44, 4, 33, 4); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (54, 4, 53, 1); 
insert into enrollment (id, student_id, section_id, grade_id) values 
    (64, 6, 53, 1) 

Answer 1

のように見える私はあなたのサンプルを試してみましたが、あなたと同じ結果を持って管理することはできません。

私はこれを試してみました：私は学生は、彼が結果になり文句を言わない何のコース

が、それは右のあなたのためですがない場合を意味している学生や入学テーブルに基づいてフィルタリング

​​

を？