最近我使用MySQL時，發(fā)現(xiàn)一個很奇怪的問題：讀取的字段值中文變成了問號。

首先我檢查了數(shù)據(jù)庫編碼，確認其為utf8mb4。

mysql>show variables like '%char%';
+--------------------------+----------------------------------------------------+
| Variable_name            | Value                                              |
+--------------------------+----------------------------------------------------+
| character_set_client     | utf8mb4                                            |
| character_set_connection | utf8mb4                                            |
| character_set_database   | utf8mb4                                             |
| character_set_filesystem | binary                                             |
| character_set_results    | utf8mb4                                            |
| character_set_server     | utf8mb4                                            |
| character_set_system     | utf8                                               |
| character_sets_dir       | /usr/local/mysql5.7/share/mysql/charsets/ |
+--------------------------+----------------------------------------------------+

然后我檢查了表和字段的編碼，也都為utf8mb4：

mysql>show create table accounts;
CREATE TABLE `accounts` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(50) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4

mysql>show full columns from accounts;
+-------+--------------+--------------------+------+-----+---------+----------------+---------------------------------+---------+
| Field | Type         | Collation          | Null | Key | Default | Extra          | Privileges                      | Comment |
+-------+--------------+--------------------+------+-----+---------+----------------+---------------------------------+---------+
| id    | int(11)      | NULL               | NO   | PRI | NULL    | auto_increment | select,insert,update,references |         |
| name  | varchar(50) | utf8mb4_general_ci | YES  |     | NULL    |                | select,insert,update,references |         |
+-------+--------------+--------------------+------+-----+---------+----------------+---------------------------------+---------+

最終，我發(fā)現(xiàn)問題出在了連接數(shù)據(jù)庫時沒有指定編碼：

$conn = new mysqli($servername, $username, $password, $dbname);
$conn->set_charset("utf8mb4");

修改后，問題解決了。