mysql - Illegal mix of collations (latin1_swedish_ci,IMPLICIT) and ...

在我的代码里有一项写入数据库的操作（使用了 flask-sqlalchemy 和 pymysql)

new_course = Course(course_name=form.course_name.data,
                                course_code=form.course_code.data,
                                file_count=0)

前一个字段可以是汉字，第二个字段必须是字母加数字组合。

然后在网站运行的时候遇到了这个错误：

(1267, u"Illegal mix of collations (latin1_swedish_ci,IMPLICIT) and (utf8_general_ci,COERCIBLE) for operation '='")

按照别人的说法我更改了几个字段的编码

mysql> SHOW VARIABLES LIKE 'collation_%';
+----------------------+-------------------+
| Variable_name        | Value             |
+----------------------+-------------------+
| collation_connection | utf8_general_ci   |
| collation_database   | latin1_swedish_ci |
| collation_server     | latin1_swedish_ci |
+----------------------+-------------------+
3 rows in set (0.00 sec)

mysql> set character_set_database =utf8;
Query OK, 0 rows affected (0.00 sec)

mysql> set character_set_results =utf8;
Query OK, 0 rows affected (0.00 sec)

mysql> set character_set_server =utf8;
Query OK, 0 rows affected (0.00 sec)

mysql> set character_set_system =utf8;
ERROR 1238 (HY000): Variable 'character_set_system' is a read only variable
mysql> SET collation_server = utf8_general_ci;
Query OK, 0 rows affected (0.00 sec)

mysql> SET collation_database = utf8_general_ci;
Query OK, 0 rows affected (0.00 sec)

mysql> exit
Bye

然而在我 exit 并重新运行网站后，这个问题还会出现，重新查看编码的时候发现编码又被改回去了，这是为什么？我需要重建数据库吗，如果需要的话应当怎么做？