In joining tables, what is typically used to link the data across tables?

In joining tables, what is typically used to link the data across tables?

• A. A key field and a foreign key
• B. A shared computed field
• C. A union operation
• D. A primary key in both tables

Answer: (D)

Linking data across tables is done through a foreign key relationship. One table has a primary key that uniquely identifies each row, and the other table includes a foreign key column that stores those same values to point to the related row. When you join, you match the foreign key value in the second table to the primary key value in the first, bringing together related data from both sides. This setup enforces referential integrity, ensuring every referenced value exists in the related table. The other ideas don’t fit the common pattern: a shared computed field isn’t a reliable or enforced link, a union merely stacks rows from similar structures and doesn’t relate individual records, and having a primary key in both tables is only a special one-to-one case and isn’t the standard mechanism for linking tables.

Linking data across tables is done through a foreign key relationship. One table has a primary key that uniquely identifies each row, and the other table includes a foreign key column that stores those same values to point to the related row. When you join, you match the foreign key value in the second table to the primary key value in the first, bringing together related data from both sides. This setup enforces referential integrity, ensuring every referenced value exists in the related table.

The other ideas don’t fit the common pattern: a shared computed field isn’t a reliable or enforced link, a union merely stacks rows from similar structures and doesn’t relate individual records, and having a primary key in both tables is only a special one-to-one case and isn’t the standard mechanism for linking tables.