开发环境:

mysql=8.0
pymql=0.8.0
sqlalchemy=1.2.4

创建数据库表项的时候出现以下错误：

(pymysql.err.InternalError) (1193, "Unknown system variable 'transaction_isolation'") (Background on this error at: http://sqlalche.me/e/2j85)

看Background的意思是这个问题是driver的问题，不是sqlalchemy的问题。
查到Django环境下的类似问题：

https://code.djangoproject.com/ticket/28804

里面提到：

    @cached_property
    def transaction_isolation_variable(self):
        return 'tx_isolation' if self.mysql_version < (5, 7, 20) or self.mysql_version > (10, 0, 10) else 'transaction_isolation'

大意就是说早起版本的mysql中用的是tx_isolation，5.7.20版本之后，用的是transaction_isolation。

于是在mysql中查询transaction_isolation

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 22
Server version: 8.0.2-dmr MySQL Community Server (GPL)

Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> SELECT @@GLOBAL.transaction_isolation, @@transaction_isolation;
ERROR 1193 (HY000): Unknown system variable 'transaction_isolation'
mysql> show variables like 't%_isolation';
+---------------+-----------------+
| Variable_name | Value           |
+---------------+-----------------+
| tx_isolation  | REPEATABLE-READ |
+---------------+-----------------+

mysql到了8.0居然跟早期版本的变量名一致，以至于driver用transaction_isolation一直有问题。

于是改用mysql的官方驱动mysql connector，还是同样的问题。无奈只好降低版本到5.7.22。

先check一下：

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 124
Server version: 5.7.22 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> show variables like 't%_isolation';
+-----------------------+-----------------+
| Variable_name         | Value           |
+-----------------------+-----------------+
| transaction_isolation | REPEATABLE-READ |
| tx_isolation          | REPEATABLE-READ |
+-----------------------+-----------------+
2 rows in set (0.01 sec)

两个变量都存在，再用pymql作为driver，成功创建table。