How do you model a one-to-one relationship in a database?

A one-to-one relationship in a database is modelled by linking two tables through a primary key-foreign key relationship.

In a relational database, a one-to-one relationship exists when one record in a table is associated with one and only one record in another table. This is achieved by creating a primary key-foreign key relationship between the two tables. The primary key is a unique identifier for a record in a table, while the foreign key in a second table is used to identify the corresponding record in the first table.

To model a one-to-one relationship, you first need to identify the two entities that have this relationship. For example, let's consider a database for a school. A student has one record in the 'Student' table and a corresponding record in the 'StudentDetails' table. The 'Student' table might contain fields like StudentID (primary key), Name, and Age. The 'StudentDetails' table could contain fields like StudentID (foreign key), Address, and ContactNumber.

The StudentID in the 'StudentDetails' table is a foreign key that links to the StudentID in the 'Student' table. This creates a one-to-one relationship between the two tables. Each student has one set of details, and each set of details belongs to one student.

It's important to note that in a one-to-one relationship, the foreign key should also be unique. This ensures that each record in the first table corresponds to exactly one record in the second table. If the foreign key is not unique, then one record in the first table could potentially correspond to multiple records in the second table, creating a one-to-many relationship instead.

In summary, a one-to-one relationship in a database is modelled by identifying two entities that have this relationship, creating a primary key in the first table, and then creating a corresponding unique foreign key in the second table. This links the two tables together, ensuring that each record in the first table corresponds to exactly one record in the second table.