问题：
I really want to know more about the update, export and the values that could be given to hibernate.hbm2ddl.auto 我真的想知道更多关于更新，导出和可以给hibernate.hbm2ddl.auto的值的更多信息
I need to know when to use the update and when not? 我需要知道何时使用更新，何时不知道？ And what is the alternative? 还有什么选择？
These are changes that could happen over DB: 这些是可能发生在DB上的变化：
- new tables 新表
- new columns in old tables 旧表中的新列
- columns deleted 列已删除
- data type of a column changed 列的数据类型已更改
- a type of a column changed its attributes 列的类型更改了其属性
- tables dropped 桌子掉了
- values of a column changed 列的值已更改
In each case what is the best solution? 在每种情况下，最佳解决方案是什么？
解决方案：
参考一： https://stackoom.com/question/1pys/Hibernate-hbm-ddl-auto配置的可能值是什么-它们做了什么参考二： https://oldbug.net/q/1pys/What-are-the-possible-values-of-the-Hibernate-hbm2ddl-auto-configuration-and-what-do-they-do
来源：oschina
链接：https://my.oschina.net/u/3797416/blog/4314521