In relational databases, what is meant by a primary key and a foreign key, and why are they important?

In relational databases, what is meant by a primary key and a foreign key, and why are they important?

• A. Foreign keys uniquely identify a record; primary keys link to other tables.
• B. A primary key uniquely identifies a record; a foreign key links to a primary key in another table; ensures relational integrity.
• C. A primary key and a foreign key are the same thing.
• D. Foreign keys uniquely identify a record; primary keys link to other tables.

Answer: (B)

The main idea being tested is how relational databases use keys to identify data and relate tables. A primary key is the unique identifier for each row in a table; its values are unique and not null, so you can reliably retrieve or reference any specific record. A foreign key is a field in a different table that points to the primary key of the first table, creating a link between related records. This setup enforces referential integrity: every value in the foreign key must correspond to an existing primary key value in the related table (unless the foreign key is allowed to be null). That means you can’t have a child record that references a non-existent parent, which keeps data consistent across tables. For example, in a Customers table, CustomerID can be the primary key; in an Orders table, CustomerID serves as a foreign key that must match a valid CustomerID from the Customers table, tying each order to a real customer. Understanding these roles helps explain why relational databases handle joins and data integrity the way they do. The other descriptions either swap the roles or claim the two keys are the same, which would miss how the linkage and identity controls actually work.

The main idea being tested is how relational databases use keys to identify data and relate tables. A primary key is the unique identifier for each row in a table; its values are unique and not null, so you can reliably retrieve or reference any specific record. A foreign key is a field in a different table that points to the primary key of the first table, creating a link between related records.

This setup enforces referential integrity: every value in the foreign key must correspond to an existing primary key value in the related table (unless the foreign key is allowed to be null). That means you can’t have a child record that references a non-existent parent, which keeps data consistent across tables. For example, in a Customers table, CustomerID can be the primary key; in an Orders table, CustomerID serves as a foreign key that must match a valid CustomerID from the Customers table, tying each order to a real customer.

Understanding these roles helps explain why relational databases handle joins and data integrity the way they do. The other descriptions either swap the roles or claim the two keys are the same, which would miss how the linkage and identity controls actually work.