A foreign key in one table must refer to:

Question

BlackTom AI · Accepted Answer

In this question, we’re evaluating what a foreign key in one table is allowed to reference.
Option 1: 'A primary key in another table' — This is the standard rule in relational databases: a foreign key must refer to a primary key (or, more generally, a candidate key) in a different table to establish a valid relationship. This ensures referential integrity between the two tables.
Option 2: 'A composite key in another table' — While a foreign key can reference a composite primary key if the referenced table uses a composite key as its primary (or candidate) key, the statement as written is too narrow and implies that only a composite key could be the target. It ignores that a simple (single-column) primary key can also be referenced, and it doesn’t specify that the reference must be to a key in another table. Therefore this is not universally correct.
Option 3: 'Any attribute in another table' — This is incorrect. A foreign key cannot reference just any attribute; it must reference a key that uniquely identifies a row in the other table (typically the primary key or another candidate key), not an arbitrary attribute.
Option 4: 'A superkey in the same table' — This is wrong because a foreign key must reference a key in a different table, not a key within the same table. Additionally, referencing a superkey from the same table would not establish the required cross-table relationship.
Overall, the most accurate and universally applicable choice is that a foreign key in one table must refer to a primary key in another table, ensuring proper cross-table referential integrity.

A foreign key in one table must refer to:

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