数据库系统概论大作业,数据库系统概论简单的问题答案，虽然不是那么好，但是记录一下下，希望被各位采纳，我会继续加油，努力学习编程知识(Introduction to database systems, large operations, database systems introduction, simple questions, answers, although not so good, but the record down, I hope you are adopted, I will continue to refuel, and strive to learn programming knowledge)