如何设计一个可扩展的MySQL表结构来实现社交分享功能？

CREATE TABLE `user` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `username` VARCHAR(50) NOT NULL,
  `passWord` VARCHAR(50) NOT NULL,
  `email` VARCHAR(50) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `username` (`username`),
  UNIQUE KEY `email` (`email`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `share` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `user_id` INT(11) NOT NULL,
  `content` TEXT NOT NULL,
  `created_at` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`),
  CONSTRAINT `fk_user_id` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `like` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `user_id` INT(11) NOT NULL,
  `share_id` INT(11) NOT NULL,
  `created_at` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`),
  CONSTRAINT `fk_like_user_id` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `fk_like_share_id` FOREIGN KEY (`share_id`) REFERENCES `share` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `comment` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `user_id` INT(11) NOT NULL,
  `share_id` INT(11) NOT NULL,
  `content` TEXT NOT NULL,
  `created_at` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`),
  CONSTRAINT `fk_comment_user_id` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `fk_comment_share_id` FOREIGN KEY (`share_id`) REFERENCES `share` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;