View-Data Center charging system and data center Charging System

View-Data Center charging system and data center Charging System
1. What is a view?

During the first data center charging system, the student information and card information were in the same table, while the data center charging system was restructured to redesign the database, student Information and card information are divided into two separate tables (following the three-paradigm design to reduce data redundancy). When we need to query the information in both tables at the same time, it is very troublesome and error-prone to separate queries from each table according to the general method. To reduce errors, we can integrate the information to be queried into a virtual table, which is a view.

Similar to a table, a view can be used for general operations (add, delete, modify, and query) on a table. A view is a virtual table defined by a query composed of SELECT statements, when you create a view through the database itself, there is a SELECT statement below

2. How to Create a view?

Take the student table and card table in the data room charging system as an example

Create View

Add the table to be used

Select fields in the table to be used

Last save View

3. Conclusion advantages of the database:

1) centralized data used by users;

2) because of the complexity of the mask database, the view separates the complexity of the database design from the user shielding;

3) simplify the management of user permissions;

4) re-organize data for output to other applications.

Note:

1) when using View query, if a new field is added to the associated database table, you must create a new view to query the new field.

2) You cannot use the DELETE statement for views that depend on multiple basic tables.

Data room billing management system

Download it online, a lot

C language room Fee Management System

C language room Fee Management System
Reward score: 0-14 days and 23 hours from the end of the problem
Requirements:
(1) Input Function: Enter the student ID, class, name, start time, and end time of several students.
(2) computing function: calculate the cost of each student's computer (calculation formula: computer cost = (End Time-Start Time) * Charging Standard (in minutes ))
(3) modification function: Modify the personal files of students on the computer (for example, add or delete)
(4) query function: query the information of students on the computer by condition (class, learner, and name), and display all the corresponding files of the students.