What field in one table uniquely identifies a row of another table?

What field in one table uniquely identifies a row of another table?

• A. Primary key
• B. Foreign key
• C. Constraints
• D. Stored locally

Answer: (B)

In relational databases, linking data across tables is done with keys. A field in one table that points to a specific row in another table is a foreign key. This foreign key references the primary key in the related table, creating a relationship and allowing you to identify which row in the second table a given row is connected to. For example, an Orders table might store CustomerID as a foreign key that references Customers.CustomerID in the Customers table. The value in Orders.CustomerID matches the unique primary key of a customer row, tying that order to the correct customer. This mechanism also enforces referential integrity, ensuring you can’t reference a non-existent row in the related table. The primary key, in contrast, uniquely identifies a row within its own table, not in another table, and constraints or stored locally don’t define the cross-table linkage described here.

In relational databases, linking data across tables is done with keys. A field in one table that points to a specific row in another table is a foreign key. This foreign key references the primary key in the related table, creating a relationship and allowing you to identify which row in the second table a given row is connected to. For example, an Orders table might store CustomerID as a foreign key that references Customers.CustomerID in the Customers table. The value in Orders.CustomerID matches the unique primary key of a customer row, tying that order to the correct customer. This mechanism also enforces referential integrity, ensuring you can’t reference a non-existent row in the related table. The primary key, in contrast, uniquely identifies a row within its own table, not in another table, and constraints or stored locally don’t define the cross-table linkage described here.