How is a many-to-one relationship represented in a database?

A many-to-one relationship in a database is represented using foreign keys in the 'many' table that reference the 'one' table.

In a relational database, a many-to-one relationship is a type of cardinality that refers to the relationship between two entities. A many-to-one relationship means that multiple records in one table are associated with a single record in another table. This relationship is implemented using a foreign key, which is a field (or collection of fields) in one table, that is used to link to the primary key in another table.

For instance, consider a database for a library. The library has many books, but each book is written by one author. In this case, the 'Books' table would have a foreign key 'AuthorID' that references the 'Authors' table. Each book record in the 'Books' table would have an 'AuthorID' that matches the 'AuthorID' of one record in the 'Authors' table. This is how the many-to-one relationship between books and authors is represented.

The foreign key constraint also maintains referential integrity in the database. This means that the database ensures that all foreign key values point to existing rows. For example, you cannot have a book with an 'AuthorID' that does not exist in the 'Authors' table. This prevents orphaned records and keeps the data consistent.

In summary, a many-to-one relationship in a database is represented by using foreign keys in the 'many' table that reference the primary key in the 'one' table. This not only establishes the relationship between the two entities but also ensures the integrity of the data.