Which relationship types exist in relational databases?

Which relationship types exist in relational databases?

• A. One-to-one
• B. One-to-many
• C. Many-to-many
• D. All of the above

Answer: (D)

In relational databases, relationships describe how rows in one table connect to rows in another. One-to-one means a single row in the first table has at most one matching row in the second, and vice versa; this pattern is often used to split data or separate sensitive fields while keeping a direct link via a foreign key. One-to-many is the most common: one row in the first table relates to many rows in the second, such as a customer having multiple orders, with the many-side table carrying a foreign key back to the one-side table. Many-to-many occurs when rows in both tables relate to many rows in the other, which is implemented with a junction table that holds foreign keys to both tables to store the associations, as in students and classes through an enrollments table. Because relational databases support all three relationship types, the correct answer is all of the above.

In relational databases, relationships describe how rows in one table connect to rows in another. One-to-one means a single row in the first table has at most one matching row in the second, and vice versa; this pattern is often used to split data or separate sensitive fields while keeping a direct link via a foreign key. One-to-many is the most common: one row in the first table relates to many rows in the second, such as a customer having multiple orders, with the many-side table carrying a foreign key back to the one-side table. Many-to-many occurs when rows in both tables relate to many rows in the other, which is implemented with a junction table that holds foreign keys to both tables to store the associations, as in students and classes through an enrollments table. Because relational databases support all three relationship types, the correct answer is all of the above.