Which statement about relationships between tables is true?

Which statement about relationships between tables is true?

• A. They require foreign keys
• B. They can be one-to-one, one-to-many, or many-to-many
• C. They are not enforceable
• D. They are defined by unique constraints

Answer: (B)

Data relationships describe how rows in one table connect to rows in another, and there are three common patterns that cover how these connections can be formed: one-to-one, one-to-many, and many-to-many. In a one-to-many setup, a single row in the first table relates to many rows in the second (for example, a department can have many employees, but each employee belongs to one department). In a many-to-many pattern, rows in both tables can relate to many rows in the other, which is typically implemented with a junction table containing foreign keys to both tables (such as students and courses with an enrollment table). In a one-to-one relationship, a row in one table matches exactly one row in the other, often enforced by placing a foreign key in one table that references the other and ensuring uniqueness. This breadth is why the statement describing all three cardinalities is the best choice. The idea that relationships require foreign keys is not universally precise—foreign keys are the usual mechanism to enforce relationships, but the concept of cardinality is about how records pair up, not just the presence of a foreign key. Likewise, saying relationships are defined by unique constraints alone misses the cross-table reference aspect, which is the essence of how relational links are formed.

Data relationships describe how rows in one table connect to rows in another, and there are three common patterns that cover how these connections can be formed: one-to-one, one-to-many, and many-to-many. In a one-to-many setup, a single row in the first table relates to many rows in the second (for example, a department can have many employees, but each employee belongs to one department). In a many-to-many pattern, rows in both tables can relate to many rows in the other, which is typically implemented with a junction table containing foreign keys to both tables (such as students and courses with an enrollment table). In a one-to-one relationship, a row in one table matches exactly one row in the other, often enforced by placing a foreign key in one table that references the other and ensuring uniqueness.

This breadth is why the statement describing all three cardinalities is the best choice. The idea that relationships require foreign keys is not universally precise—foreign keys are the usual mechanism to enforce relationships, but the concept of cardinality is about how records pair up, not just the presence of a foreign key. Likewise, saying relationships are defined by unique constraints alone misses the cross-table reference aspect, which is the essence of how relational links are formed.