Excel VBA 教程

https://www.w3cschool.cn/excelvba/  Excel VBA 编程教程

https://www.yiibai.com/vba   VBA教程

http://www.accessoft.com/article-show.asp?id=16502   关于VBA的0、""(空字符串)、Null、Empty、与 Nothing 的区别

https://docs.microsoft.com/zh-CN/office/vba/library-reference/concepts/getting-started-with-vba-in-office    Office VBA 入门