Answer
A composite key uses more than one column to identify or constrain a row. • The uniqueness rule applies to the column combination. • It is useful when no single column identifies the relationship. • Foreign keys referencing it must use compatible referenced columns.
💡 SQL Example
CREATE TABLE enrollments (student_id integer, course_id integer, PRIMARY KEY (student_id, course_id));
Result
CREATE TABLE
⚡ Quick Revision
A composite key identifies rows through a combination of columns.