When would you use a composite primary key? Group of answer choices

a. Multi-field attributes

b. A ternary relationship

c. A unary relationship

d. A many-to-many relationship

A. Multi-field attributes

B. A ternary relationship

C. A unary relationship

d. A many-to-many relationship

Explanation:

A composite primary key is the key that uses two or more attributes to uniquely identify any row in a table. These are usually used in associative entity table in which many to many relationship between 2 or more other table exists.

Example:

Suppose we have a table which consists of 4 columns:

student_ID, subject_ID, subject_name and marks.

Here the student_ID and subject_ID can be combined together to form the composite primary key.