CREATE TABLE chat_mysql.users (
    username VARCHAR(50) PRIMARY KEY,
    password VARCHAR(255) NOT NULL
);
SET SQL_SAFE_UPDATES = 0;
DELETE FROM chat_mysql.users;
SET SQL_SAFE_UPDATES = 1;
INSERT INTO chat_mysql.users (username, password)
VALUES
('admin', '123'),
('query', '123'),
('tom', '123'),
('jack', '123'),
('lucy', '123'),
('lily', '123');
select * from chat_mysql.users;


CREATE TABLE chat_mysql.contacts (
    user_name VARCHAR(50) NOT NULL,
    contact_name VARCHAR(50) NOT NULL,

    PRIMARY KEY (user_name, contact_name),

    FOREIGN KEY (user_name)
        REFERENCES chat_mysql.users(username),

    FOREIGN KEY (contact_name)
        REFERENCES chat_mysql.users(username)
);
INSERT INTO chat_mysql.contacts (user_name, contact_name)
VALUES
('admin', 'query'),
('admin', 'tom'),
('admin', 'jack'),
('admin', 'lucy'),
('query', 'admin'),
('query', 'tom'),
('tom', 'admin'),
('tom', 'query'),
('admin', 'lily'),
('lily', 'admin');
select * from chat_mysql.contacts;

CREATE TABLE chat_mysql.messages (
    id INT PRIMARY KEY AUTO_INCREMENT,
    message_id VARCHAR(64) NOT NULL,
    sender_name VARCHAR(50) NOT NULL,
    receiver_name VARCHAR(50) NOT NULL,
    content VARCHAR(1000) NOT NULL,
    created_at DATETIME DEFAULT CURRENT_TIMESTAMP,

    FOREIGN KEY (sender_name)
        REFERENCES chat_mysql.users(username),

    FOREIGN KEY (receiver_name)
        REFERENCES chat_mysql.users(username)
);