问题：
I really want to know more about the update, export and the values that could be given to hibernate.hbm2ddl.auto我真的很想知道更多关于更新、导出和可以给hibernate.hbm2ddl.auto的值
I need to know when to use the update and when not?我需要知道何时使用更新，何时不使用？ And what is the alternative?什么是替代方案？
These are changes that could happen over DB:这些是可能发生在 DB 上的更改：
- 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一种类型的列改变了它的属性
- 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://en.stackoom.com/question/1pys参考二： https://stackoom.com/question/1pys