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<>概念
事务：是一套完整的业务逻辑，在这套业务逻辑中可能包含多天SQL语句，这些SQL语句要么都成功，要么都失败
举例：张三给李四转账100元。
<>特征
原子性(Atomicity)： 事务中包含的操作被看做一个逻辑单元，这个逻辑单元中的操作要么全部成功，要么全部失败
一致性(Consistency)：事务的结果保留不变，即事务的运行并不改变数据的一致性
隔离性(Isolation)：又称孤立性，事务的中间状态对其它事务是不可见的
持久性(Durability)：指一个事务一旦提交成功，它对数据库中数据的改变就应该是永久性的
<>事务提交机制
* 概念
提交: 将内存中的修改写入数据库
回滚: 拒绝将内存中的修改写入数据库
* 方式
提交:
方式1: 手动提交 连接对象.commit()
方式2: 自动提交 创建连接 autocommit=True
回滚:
方式1: 默认情况下，在 pymysql 不提交就回滚
方式2: 手动回滚 连接对象.rollback()
<>事务操作
需求:先往 t_book 表插入书的信息，然后向 t_hero 插入该书主角的信息，要求，要么都成功，要么都失败
核心知识点: 事务的实现(通用模板)
事务操作需要使用try控制分支使用if else不可以
try: sql1 = "xxxx" cursor.execute(sql1) sql2 = "yyy" cursor.execute(sql2) conn.
commit() # 事务提交 except Exception as e: conn.rollback() # 事务回滚 finally: # 5.释放资源
cursor.close() conn.close()
