llaves - SQL - 18 dec

gistfile1.txt

-- Users
DROP TABLE users;

-- ID strings -- x ()

-- ADMIN - 1
-- SOFT delete
CREATE TABLE users(
    id INT AUTO_INCREMENT PRIMARY KEY, -- Indexados -- COUNT(id) -- COUNT(username)
    username VARCHAR(50) NOT NULL,
    first_name VARCHAR(100),
    last_name VARCHAR(100)
);

INSERT INTO users (username, first_name, last_name) VALUES ('cody1', 'Cody', 'Cody'); -- 1
INSERT INTO users (username, first_name, last_name) VALUES ('cody2', 'Cody', 'Cody');
INSERT INTO users (username, first_name, last_name) VALUES ('cody3', 'Cody', 'Cody');
INSERT INTO users (username, first_name, last_name) VALUES ('cody4', 'Cody', 'Cody');
INSERT INTO users (username, first_name, last_name) VALUES ('cody5', 'Cody', 'Cody'); -- 5

-- 1: M
-- BELONGS to
DROP TABLE tasks;

CREATE TABLE tasks(
    id INT AUTO_INCREMENT PRIMARY KEY,
    user_id INT,
    title VARCHAR(50),
    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE --En pertenencia
);

INSERT INTO tasks(user_id, title) VALUES (6, 'Terminar el curso');
INSERT INTO tasks(user_id, title) VALUES (6, 'Practicar');
INSERT INTO tasks(user_id, title) VALUES (6, 'Apagar la instancia de AMAZON!!!! $');

-- TRUNCATE users;
-- Courses 
DROP TABLE courses;

CREATE TABLE courses(
    id INT AUTO_INCREMENT PRIMARY KEY,
    title VARCHAR(100) NOT NULL
);

INSERT INTO courses(title) VALUES ('Base de datos'); -- 1
INSERT INTO courses(title) VALUES ('Python');
INSERT INTO courses(title) VALUES ('Ruby');
INSERT INTO courses(title) VALUES ('Rust'); -- 4

-- Enrollments
-- M:M
-- Un usuario puede poseer múltiples cursos
-- Un curso puede ser tomado por múltiples usuarios

DROP TABLE enrollments;

-- M:M
CREATE TABLE enrollments(
    id INT AUTO_INCREMENT PRIMARY KEY,
    user_id INT, -- FK
    course_id INT, -- FK
    -- attempts: INT
    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE,
                                            -- ON DELETE SET NULL
    FOREIGN KEY (course_id) REFERENCES courses(id) ON DELETE CASCADE
);
INSERT INTO enrollments (user_id, course_id) VALUES(2, 1);

-- @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=1


-- SELECT
-- JOINs

-- INNER JOIN
-- LEFT JOIN 
-- RIGHT JOIN

-- CROSS JOIN

-- SELECT 
--    *
-- FROM users FULL JOIN tasks

SELECT 
    *
FROM users INNER JOIN tasks ON users.id = tasks.user_id;
WHERE users.username = 'cody6';