Which statement correctly differentiates a primary key from a foreign key?

Which statement correctly differentiates a primary key from a foreign key?

• A. Primary key uniquely identifies a row; a foreign key links to a primary key in another table to establish relationships.
• B. Primary key links to another table; foreign key uniquely identifies a row.
• C. Primary key stores data; foreign key stores metadata.
• D. Primary key is only in child tables; foreign key is only in parent tables.

Answer: (A)

In relational databases, the primary key uniquely identifies a row within its own table, while a foreign key creates a link to a row in another table by referencing that table’s primary key. This combination allows each record to be both uniquely identifiable locally and related to related data elsewhere. For example, a Customers table uses CustomerID as the primary key; an Orders table includes CustomerID as a foreign key that points to Customers.CustomerID, tying each order to a real customer and enforcing referential integrity. Primary keys must be unique and not null; foreign keys must match an existing value in the referenced table (though they can be duplicates across different rows and may be null if the relationship is optional). The other options reverse roles or misstate what keys do (storing data or metadata, or being confined to parent/child tables), which doesn’t reflect how keys function in relational design.

In relational databases, the primary key uniquely identifies a row within its own table, while a foreign key creates a link to a row in another table by referencing that table’s primary key. This combination allows each record to be both uniquely identifiable locally and related to related data elsewhere. For example, a Customers table uses CustomerID as the primary key; an Orders table includes CustomerID as a foreign key that points to Customers.CustomerID, tying each order to a real customer and enforcing referential integrity. Primary keys must be unique and not null; foreign keys must match an existing value in the referenced table (though they can be duplicates across different rows and may be null if the relationship is optional). The other options reverse roles or misstate what keys do (storing data or metadata, or being confined to parent/child tables), which doesn’t reflect how keys function in relational design.