SQL链接

https://blog.csdn.net/shaiguchun9503/article/details/82349050  （ROW_NUMBER、RANK、DENSE_RANK、NTILE）简介

https://www.cnblogs.com/godbell/p/9332885.html       SQL ROUND函数

https://www.cnblogs.com/wangjiming/p/10098061.html  SQL基础