To do a project, the database design must be indispensable! In the learning stage, it is basically a single table. However, in the actual development process, one-to-many and many-to-many tables are everywhere! Simply organize, one-to-many, many-to-many table how to design and organize ideas:
There are three correspondences between database entities: one-to-one, one-to-many, and many-to-many.
An example of a one-to-one relationship:
- One student corresponds to one student file material, or each person has a unique ID number.
Example of a one-to-many relationship:
- A student belongs to only one class, but a class has multiple students.
Example of many-to-many relationship:
- A student can choose multiple courses, and a course can have multiple students.
1. One-to-many relationship processing:
Learn one-to-many with student and class questions:
Design database table: just add an ID of the class number to the student table ;
Note: When you are a beginner in the table in the database, you should add primary and foreign key constraints to avoid data confusion when deleting data!
2. Many-to-many relationship processing:
Learn how to deal with many-to-many problems through student selection:
In many-to-many, adding a field to a table will not work, so when dealing with many-to-many table problems, it is necessary to consider establishing a relationship table
example:
Student table: 
Class table: 
Relation table:
Note: So for many-to-many tables, the relationship between the two tables is established through the relationship table! After establishing the primary foreign key in the many-to-many table, delete the content of the constraint table first and then delete the content of the main table