mysql utf8mb4乱码问题

mysql> SHOW VARIABLES WHERE Variable_name LIKE 'character_set_%' OR Variable_name LIKE 'collation%';
+--------------------------+-----------------------------------+
| Variable_name | Value |
+--------------------------+-----------------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | utf8 |
| character_set_system | utf8 |
| character_sets_dir | /home/mysql/mysql/share/charsets/ |
| collation_connection | utf8_general_ci |
| collation_database | utf8_general_ci |
| collation_server | utf8_general_ci |
+--------------------------+-----------------------------------+

表定义：
mysql> SHOW CREATE DATABASE xxx;
+------------------------+---------------------------------------------------------------------------------+
| Database | Create Database |
+------------------------+---------------------------------------------------------------------------------+
| xxx | CREATE DATABASE xxx /*!40100 DEFAULT CHARACTER SET utf8 */ |
+------------------------+---------------------------------------------------------------------------------+
表字段定义utf8mb4
CREATE TABLE xxx (
id int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT '自增id',
content mediumtext COLLATE utf8mb4_unicode_ci NOT NULL COMMENT '问题描述',
) ENGINE=InnoDB AUTO_INCREMENT=3823 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci COMMENT=''

解决方案：

set names utf8mb4;（设置character_set_client character_set_server 为mb4。）