如何通过ASP.NET中的C＃从数据库中的列获取平均值？

I'm very new to C# and working in ASP.NET, and I'm supposed to get all the information from a table in a local database that I have connected with in Visual Studio. All I really know is how to connect and how to get the whole table in a grid view, but I would in the end of the grid view, or maybe in some other way to show the medium value for each column. I'm very new to C# and working in ASP.NET, and