Mysql如何处理插入4个字节的字符呢？

新版WordPress就是用了utf8mb4编码：

/* 数据库 */
CREATE DATABASE IF NOT EXISTS `wordpress` 
DEFAULT CHARACTER SET utf8 
COLLATE utf8_general_ci; 
/* 评论表 */
CREATE TABLE IF NOT EXISTS `wp_comments` (
  `comment_ID` bigint(20) unsigned NOT NULL,
  `comment_post_ID` bigint(20) unsigned NOT NULL DEFAULT '0',
  `comment_author` text COLLATE utf8mb4_unicode_ci NOT NULL,
  `comment_author_email` varchar(100) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
  `comment_author_url` varchar(200) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
  `comment_author_IP` varchar(100) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
  `comment_date` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `comment_date_gmt` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `comment_content` mediumtext COLLATE utf8mb4_unicode_ci NOT NULL,
  `comment_karma` int(11) NOT NULL DEFAULT '0',
  `comment_approved` varchar(20) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '1',
  `comment_agent` varchar(255) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
  `comment_type` varchar(20) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
  `comment_parent` bigint(20) unsigned NOT NULL DEFAULT '0',
  `user_id` bigint(20) unsigned NOT NULL DEFAULT '0'
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_un