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
• List all the students and their classes and rename the columns to "student" and "class"
• List all the students and their average grade
• List all the students and a count of how many classes they are currently enrolled in
• List all the students and their class count IF they are in more than 2 classes
• List all the teachers for each student
• List all the teachers for each student grouped by each student
• Find the average grade for a each class
• List students' name and their grade IF their grade is lower than the average.

@TravisGM92 - Mine worked with changing the name to just 'class' - I didn't get errors or anything flagged that it was a reserved word.

Unsure what the comment above you is about: is it saying they got an error? Is it saying this isn't best practice/convention?

@TravisGM92 - Mine worked with changing the name to just 'class' - I didn't get errors or anything flagged that it was a reserved word.

Unsure what the comment above you is about: is it saying they got an error? Is it saying this isn't best practice/convention?

@priyapower, yeah sometimes SQL won't let me use a particular word to rename a column to cause it'll confuse it with something else. I'm imagining they had that issue, calling a column 'class' would confuse SQL so it prompts you to use a different word. I've had it happen, although it didn't happen with me this time.

And I think they're saying they got an error...

I believe the varying issue depends on whether you are using the shorthand. If you specify SELECT c.name AS class it runs without an error, but it does error if you try to use the shorthand SELECT c.name class.