CREATE TABLE IF NOT EXISTS `ai_chat_session` (
  `id` bigint NOT NULL AUTO_INCREMENT COMMENT '主键',
  `memory_id` varchar(64) NOT NULL COMMENT '会话ID',
  `user_id` bigint NOT NULL COMMENT '用户ID',
  `tenant_id` bigint DEFAULT NULL COMMENT '租户ID',
  `title` varchar(128) DEFAULT NULL COMMENT '会话标题',
  `last_message` varchar(512) DEFAULT NULL COMMENT '最后一条消息',
  `message_count` int NOT NULL DEFAULT 0 COMMENT '消息数量',
  `last_chat_time` datetime DEFAULT NULL COMMENT '最后聊天时间',
  `create_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
  `update_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
  PRIMARY KEY (`id`),
  UNIQUE KEY `uk_ai_chat_session_memory_id` (`memory_id`),
  KEY `idx_ai_chat_session_user_tenant` (`user_id`, `tenant_id`),
  KEY `idx_ai_chat_session_last_chat_time` (`last_chat_time`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci COMMENT='AI历史会话元数据表';