What is a composite key in database design?

A composite key is defined as a key that consists of two or more attributes that together uniquely identify a record in a database table. This means that no single attribute is sufficient on its own to uniquely distinguish a record, but when combined, these attributes form a unique identifier for each entry.

The use of composite keys is particularly important in situations where an individual field might have duplicates, such as in a many-to-many relationship. By combining multiple fields, the database can enforce uniqueness and maintain data integrity. For instance, in a student-course enrollment system, a composite key could be formed by combining the student ID and the course ID, ensuring that each student-course pairing is unique.

Understanding composite keys is essential for designing normalized databases and for ensuring proper relationships between tables in relational database management systems.