PHP simple chat

DB struct

CREATE DATABASE `neoma158_simplechat` /*!40100 DEFAULT CHARACTER SET utf8 */;

CREATE TABLE `fastauth` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `user` int(10) unsigned NOT NULL,
  `key` varchar(32) NOT NULL,
  `available` int(10) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `key_UNIQUE` (`user`,`key`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

CREATE TABLE `messages` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `user` int(11) NOT NULL,
  `message` varchar(1024) NOT NULL,
  `timestamp` int(10) unsigned NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

CREATE TABLE `sessions` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `user` int(10) unsigned NOT NULL,
  `v` varchar(32) NOT NULL,
  `expires` int(10) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `v_UNIQUE` (`v`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

CREATE TABLE `users` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `login` varchar(45) NOT NULL,
  `password` varchar(32) NOT NULL,
  `lastactivity` int(10) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `login_UNIQUE` (`login`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;