What is the difference between M and C in MVC mode?

What is the difference between M and C in MVC mode? What is the difference between M and C in MVC mode? For example, to create a student information management system, M can add, delete, modify, and query student information and operate databases. So what else does layer C need? Of course, the C layer can also use SQL to operate databases.

Reply to discussion (solution)

The mvc division of labor is divided by humans and there is no clear boundary
Generally, M is the business logic. That is, all business-related parts (except the user interface) should be placed here
Because the database is related to specific services, it should not be placed in C (not to say that C cannot operate the database, but you force yourself to access the database not in C)

M is the data layer for data acquisition.
C is the control layer for logical control.

This is understandable.

M is data, C is to control how to use data, and V is to display data.

The mvc division of labor is divided by humans and there is no clear boundary
Generally, M is the business logic. That is, all business-related parts (except the user interface) should be placed here
Because the database is related to specific services, it should not be placed in C (not to say that C cannot operate the database, but you force yourself to access the database not in C)

+ 1 some open-source code feel that the difference between M and C is not big. the methods written in M can also be written in C, and those written in C can also be placed in M, so I am always confused about the difference.