What does a bridge (junction) table typically contain?

• A. The primary keys of the related tables as foreign keys and possibly extra attributes.
• B. Only a single primary key column.
• C. Only non-key attributes.
• D. Only one row per related pair.

Answer: (A)

A bridge table is used to implement many-to-many relationships by storing the identifiers from both related tables. It holds the primary keys of the two tables as foreign keys, and these two keys together identify each link in the relationship. Often the two foreign keys form a composite primary key, though some designs use a separate surrogate key. In addition to the keys, the bridge table can include extra attributes that describe the relationship itself (for example, a timestamp, quantity, or status that applies to that specific pairing). This combination of the two foreign keys and any optional attributes is what defines the bridge table’s role. It isn’t just a single primary key column, nor is it limited to non-key attributes, because the foreign keys are essential to linking the related records. While a junction table typically represents one row per related pair, the defining feature remains the pair of foreign keys that connect the two tables.