Primary Key and Foreign Key Relationship

Primary key and foreign key are two important concepts in relational database management systems. A primary key is a unique identifier for a record in a table, while a foreign key is a field in a table that refers to the primary key of another table. When a primary key is combined with a foreign key, it creates a parent-child relationship between the tables that connect them.

Parent-Child Relationship

A parent-child relationship is a type of hierarchical relationship between two tables, where one table (the parent) is related to one or more records in another table (the child). The primary key of the parent table is used as the foreign key in the child table to establish this relationship. The child table depends on the parent table for its existence and cannot exist without it. In other words, the child table is a subset of the parent table.

For example, consider two tables, one for customers and another for orders. The customers table has a primary key called CustomerID, and the orders table has a foreign key called CustomerID that refers to the CustomerID field in the customers table. This creates a parent-child relationship between the two tables, where each customer can have one or more orders, and each order belongs to one customer.

Many-to-Many Relationship

A many-to-many relationship is a type of relationship between two tables, where one record in a table can be related to many records in another table, and vice versa. This type of relationship requires a third table, called a junction table or bridge table, to connect the two tables. The primary keys of the two tables become foreign keys in the junction table.

Network Model

The network model is a type of database model that represents data as a network of interconnected records. This model was popular in the 1960s and 1970s but has been largely replaced by the relational model. It does not use primary keys and foreign keys to establish relationships between tables.

Conclusion

In conclusion, when a primary key is combined with a foreign key, it creates a parent-child relationship between the tables that connect them. This relationship is a type of hierarchical relationship, where one table is the parent and another table is the child. It is not a many-to-many relationship or a network model.

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