Summarize one-to-many, many-to-one or one-to-many relationships in the database

one-to-many, many -to one or one-to-many relationships in a database

Association mappings: one-to-many/many-

The most common mapping is the relationship between players and the team;

One-to-many: from a team point of view, a team with multiple players is a one-to-many

Many-to-one: from a player's point of view, multiple players belong to a team

A one-to-many relationship between data tables such as:

Association mappings: one-to-one

One to one relationship is the relationship between the team and the team's address, a team only has an address, and an address area has only one team.

There are two kinds of data table-to-one relationships: a foreign key association and a primary key association. This is illustrated below:

One-to-one foreign key association:

Two-to-one primary key association: requires that the primary key of both tables be exactly the same, and that the correlation is established by the primary key of two tables

Association mappings: Many-to-many

Many-to-many relationships are also common, such as the relationship between students and electives, where a student can choose multiple elective courses, and each elective can be selected by more than one student.

Many-to-many association relationships in a database are generally handled in the form of intermediate tables, converting many-to-many to two-to-many.

Many-to-many relationships between data tables such as:

Summarize one-to-many, many-to-one or one-to-many relationships in the database