psql

qq=# CREATE DATABASE test_guru;

                                ----- CREATE TABLE -----

qq=# CREATE TABLE categories (
qq(# id serial PRIMARY KEY,
qq(# title text NOT null
qq(# );

qq=# CREATE TABLE tests (
qq(# id serial PRIMARY KEY,
qq(# title text NOT null,
qq(# level int NOT null,
qq(# category_id int NOT null
qq(# );

qq=# CREATE TABLE questions (
qq(# id serial PRIMARY KEY,
qq(# body text NOT null,
qq(# test_id int NOT null
qq(# );

                                ----- INSERT -----

qq=# INSERT INTO categories(title) VALUES
qq-# ('android'),
qq-# ('linux'),
qq-# ('macos');

qq=# INSERT INTO tests(title, level, category_id) VALUES
qq-# ('Xcode', 1, 3),
qq-# ('App Store', 2, 3),
qq-# ('Google Play', 3, 1),
qq-# ('Центр приложений', 1, 2),
qq-# ('Kotlin', 3, 1);

qq=# INSERT INTO questions(body, test_id) VALUES
('Язык программирования?', 5),
('Магазин приложений?', 2),
('Java совместимый язык?', 5),
('IDE работает только под macos?', 1),
('Какой-то вопрос', 3);

                                ----- SELECT -----

qq=# SELECT *
qq-# FROM tests
qq-# WHERE level IN (2,3);

qq=# SELECT *
qq-# FROM questions
qq-# WHERE test_id = 5;

                                ----- UPDATE -----

qq=# UPDATE tests
qq-# SET title = 'Software center', level = 3
qq-# WHERE title = 'Центр приложений';

                                ----- DELETE -----

qq=# DELETE
qq-# FROM questions
qq-# WHERE test_id = 1;

                                ----- JOIN -----

qq=# SELECT tests.title AS tests, categories.title AS categories
qq-# FROM tests
qq-# JOIN categories
qq-# ON tests.category_id = categories.id;

qq=# SELECT questions.body, tests.title
qq-# FROM questions
qq-# JOIN tests
qq-# ON questions.test_id = tests.id;