Intermediate SQL

intermediate_sql.md

Intermediate SQL Workshop

• Run psql
• You may need to run CREATE DATABASE intermediate_sql;
• To exit this shell, you can run CTRL d

Create tables

Let's create some tables in the database.

CREATE TABLE students(id SERIAL, name TEXT);
CREATE TABLE classes(id SERIAL, name TEXT, teacher_id INT);
CREATE TABLE teachers(id SERIAL, name TEXT, room_number INT);
CREATE TABLE enrollments(id SERIAL, student_id INT, class_id INT, grade INT);

Add data

Let's insert some students.

INSERT INTO students (name)
VALUES ('Penelope'),
       ('Peter'),
       ('Pepe'),
       ('Parth'),
       ('Priscilla'),
       ('Pablo'),
       ('Puja'),
       ('Patricia'),
       ('Piper'),
       ('Paula'),
       ('Pamela'),
       ('Paige'),
       ('Peggy'),
       ('Pedro'),
       ('Phoebe'),
       ('Pajak'),
       ('Parker'),
       ('Priyal'),
       ('Paxton'),
       ('Patrick');

Let's add some teachers.

INSERT INTO teachers (name, room_number)
VALUES ('Phillips', 456),
       ('Vandergrift', 120),
       ('Mauch', 101),
       ('Patel', 320),
       ('Marquez', 560),
       ('Boykin', 200),
       ('Phlop', 333),
       ('Pendergrass', 222),
       ('Palomo', 323),
       ('Altshuler', 543),
       ('Aleman', 187),
       ('Ashley', 432),
       ('Bonacci', 399),
       ('Brazukas', 287),
       ('Brockington', 299),
       ('Brizuela', 376),
       ('Burkhart', 199),
       ('Choi', 463),
       ('Shah', 354),
       ('Dimaggio', 251);

Let's add some classes.

INSERT INTO classes (name, teacher_id)
VALUES ('Cooking Pasta', 1),
       ('Yoga', 1),
       ('How to Guitar', 2),
       ('Gym', 3),
       ('Football', 4),
       ('Calculus', 5),
       ('Fruit', 6),
       ('Social Studies', 7),
       ('English', 8),
       ('Programming', 9),
       ('Singing', 10),
       ('Fashion', 11);

Lastly, let's add some enrollments!

INSERT INTO enrollments (student_id, class_id, grade)
VALUES (1, 1, 60),
       (2, 2, 70),
       (2, 4, 100),
       (3, 2, 74),
       (4, 3, 82),
       (5, 3, 45),
       (5, 4, 50),
       (7, 11, 62),
       (7, 10, 76),
       (7, 9, 81),
       (7, 8, 91),
       (8, 8, 84),
       (9, 8, 88),
       (9, 7, 83),
       (10, 7, 93),
       (10, 5, 95),
       (11, 5, 95),
       (11, 11, 80),
       (11, 6, 95),
       (11, 1, 94),
       (11, 2, 60),
       (12, 6, 55),
       (13, 7, 97),
       (14, 10, 86),
       (15, 9, 77),
       (15, 4, 93),
       (15, 1, 73),
       (16, 2, 79),
       (16, 6, 73),
       (17, 7, 86),
       (17, 8, 91),
       (17, 9, 93),
       (18, 10, 94),
       (19, 4, 84),
       (20, 1, 85),
       (20, 11, 89),
       (20, 3, 98);

Practice!!

• List all the students and their classes

SELECT students.name AS student_name, classes.name AS class_name FROM enrollments INNER JOIN students ON enrollments.student_id = students.id INNER JOIN classes ON enrollments.class_id = classes.id;

• List all the students and their classes and rename the columns to "student" and "class"
• List all the students and their average grade

SELECT students.name AS student, avg(grade) AS average FROM enrollments INNER JOIN students ON enrollments.student_id = students.id GROUP BY students.name;

• List all the students and a count of how many classes they are currently enrolled in

SELECT students.name AS student, count(classes) AS classes FROM enrollments INNER JOIN students ON enrollments.student_id = students.id INNER JOIN classes ON enrollments.class_id = classes.id GROUP BY students.name;

• List all the students and their class count IF they are in more than 2 classes

SELECT students.name AS students, count(classes) AS class_count FROM enrollments INNER JOIN students ON enrollments.student_id = students.id INNER JOIN classes ON enrollments.class_id = classes.id GROUP BY students.name HAVING count(classes) > 2;

• List all the teachers for each student

SELECT students.name AS student, teachers.name AS teacher FROM enrollments INNER JOIN students ON enrollments.student_id = students.id INNER JOIN classes ON enrollments.class_id = classes.id INNER JOIN teachers ON classes.teacher_id = teachers.id;

• List all the teachers for each student grouped by each student

SELECT students.name AS student, teachers.name AS teacher FROM enrollments INNER JOIN students ON enrollments.student_id = students.id INNER JOIN classes ON enrollments.class_id = classes.id INNER JOIN teachers ON classes.teacher_id = teachers.id GROUP BY students.name, teachers.name;

• Find the average grade for a each class

SELECT classes.name AS class, avg(grade) AS average FROM enrollments INNER JOIN classes ON enrollments.class_id = classes.id GROUP BY class;

• List students' name and their grade IF their grade is lower than the average.