Looking at your question, I think what you need should be the data types of these fields in the database, right?

Account varchar(20)-20)-A variable-length string of less than 20 characters. Of course, you can change the length yourself.

Password varchar(30)

Role name nvarchar(20)-20)-A variable-length string of less than 20 characters. Because it may contain Chinese, double-byte storage is better.

The student number int or varchar( 10) can be numbered with integers or strings with a specific structure according to the specific situation.

The student number char( 10) is generally a string with a fixed length, and the length should be changed to an appropriate value.

Name nvarchar(20)

Gender bit or char(2) bit has only two values (0, 1), which can represent male and female respectively, or can directly save' male/female'.

National female architect (20)

Address nvarchar(50)

The telephone varchar( 13) can be a mobile phone number or a fixed line.

Role int or varchar(20) if there is a role table, it can be a role ID or a role name directly.

Postal code char(6) Postal code has 6 fixed digits.

Class int or nvarchar(20) if there is a class table, it can be directly a class ID or a class name.

Note text or nvarchar(255) Note If there is no length limit, you can use text.

Photo nvarchar(255) or image can only save the image path, or directly save the data stream.

Theme int or nvarchar(20)

Subject note text or nvarchar(255)

Grade number int or varchar( 10)

Semester int or nvarchar(20) can be used to represent semesters by numbers, or words can be saved.

Course int or nvarchar(20) can be ID or name.

Grade integral

System management. What is this?

Class number int or char( 10)

Class name nvarchar(20)

Special course int or nvarchar(20)

Teacher int or nvarchar(20) can be ID or name.

Registration time date time

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If it is really used in C# code, int is still int, datetime is still datetime, char and varchar and nvarchar just turn to string.