mysql 修改字段的字符集

mysql> desc t1;
+----------+----------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| userid | int(11) | YES | | NULL | |
| username | varchar(20000) | YES | | NULL | |
+----------+----------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

 

mysql> alter table t1 change username username varchar(200) charset utf8mb4;
Query OK, 0 rows affected (0.11 sec)
Records: 0 Duplicates: 0 Warnings: 0