text: CREATE TABLE user (
      id INT PRIMARY KEY AUTO_INCREMENT,
      login VARCHAR(60),
      password VARCHAR(60),
      root_directory INT DEFAULT NULL
  );
  
  CREATE TABLE directory (
      id INT PRIMARY KEY AUTO_INCREMENT,
      name VARCHAR(60),
      parent INT NOT NULL,
      user INT NOT NULL
  );
  
  CREATE TABLE file (
      id INT PRIMARY KEY AUTO_INCREMENT,
      name VARCHAR(100),
      directory INT NOT NULL
  );
  
  CREATE TABLE file_version (
      id INT PRIMARY KEY AUTO_INCREMENT,
      file INT NOT NULL,
      path VARCHAR(255),
      uploaded_on TIMESTAMP DEFAULT CURRENT_TIMESTAMP()
  );
  
  ALTER TABLE file ADD CONSTRAINT FOREIGN KEY (directory) REFERENCES directory(id);
  ALTER TABLE directory ADD CONSTRAINT FOREIGN KEY (user) REFERENCES user(id);
  ALTER TABLE file_version ADD CONSTRAINT FOREIGN KEY (file) REFERENCES file(id);