Foreign Key and Primary Key Relationship

Foreign Key and Primary Key relationship in a database creates a network model between tables that connect them. A foreign key is a field or a set of fields in one table that refers to the primary key in another table. This relationship establishes a connection between the two tables, allowing for data integrity and efficient data retrieval.

1. Primary Key:
A primary key is a unique identifier for each record in a table. It ensures that each record in the table is uniquely identifiable and serves as a reference for other tables. The primary key constraint is used to enforce this uniqueness and is typically applied to one or more fields in a table.

2. Foreign Key:
A foreign key is a field or a set of fields in one table that refers to the primary key in another table. It establishes a link between the two tables, allowing for the enforcement of referential integrity. The foreign key constraint ensures that the values in the foreign key field(s) match the values in the referenced primary key field(s) or are NULL.

Network Model between Tables:

When a foreign key is combined with a primary key, it creates a network model between the tables that connect them. This network model represents the relationships between tables in a database.

1. One-to-One Relationship:
A foreign key can be used to establish a one-to-one relationship between two tables. In this type of relationship, each record in one table is associated with exactly one record in the other table. Example: Employee and EmployeeDetails tables, where each employee has unique details.

2. One-to-Many Relationship:
A foreign key can also establish a one-to-many relationship between two tables. In this type of relationship, each record in the primary table can be associated with multiple records in the related table. Example: Customer and Orders tables, where one customer can have multiple orders.

3. Many-to-Many Relationship:
A many-to-many relationship can be implemented using a junction table, which includes the primary keys of the two tables involved. The foreign keys in the junction table connect the primary keys of the related tables. Example: Student and Course tables, where each student can be enrolled in multiple courses, and each course can have multiple students.

Conclusion:

In summary, when a foreign key is combined with a primary key, it creates a network model between tables that connect them. This network model represents the relationships between tables, such as one-to-one, one-to-many, or many-to-many, and ensures data integrity and efficient data retrieval in a database.