How does a relational database manage relationships between different tables?

A relational database manages relationships between tables using keys, specifically primary and foreign keys.

In a relational database, data is organised into tables, each having a unique identifier known as a primary key. This primary key is used to uniquely identify each record in a table. Relationships between different tables are established using these primary keys and another type of key known as a foreign key. A foreign key is a field (or collection of fields) in one table, that is used to link to the primary key in another table.

The table containing the foreign key is called the child table, and the table containing the candidate key is called the parent table. These keys allow databases to match related data across tables, enabling the combination of data from two or more tables through the use of a single database query. This is a fundamental aspect of the relational database model, which organises data into tables that are related by common fields.

There are several types of relationships that can be established between tables in a relational database. The most common are one-to-one, one-to-many, and many-to-many. In a one-to-one relationship, each row in the first table is linked to one and only one row in the second table. In a one-to-many relationship, a single row in the first table can be related to one or more rows in the second table. In a many-to-many relationship, multiple records in a table can be associated with multiple records in another table.

The management of these relationships is crucial for maintaining data integrity within the database. For instance, the database system enforces referential integrity rules to ensure that these relationships are preserved. This means that the database will prevent any changes that would lead to inconsistent data. For example, if a record in a parent table is deleted, the database system will also delete any related records in the child table, or it will prevent the deletion if there are related records.

In summary, a relational database manages relationships between different tables using keys and referential integrity rules. This allows for efficient querying and ensures the consistency and reliability of the data stored within the database.