Which of the following is NOT true about a foreign key that connects two tables in a database?

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BlackTom AI · Accepted Answer

Question restatement: Which of the following is NOT true about a foreign key that connects two tables in a database?

Option 1: "it must be a primary key in at least one of the tables". This is false because a foreign key in the child table doesn't have to be a primary key anywhere; it must reference a candidate key (often the primary key) in the parent table, but the foreign key column itself need not be a primary key in either table.

Option 2: "it must be of the same data type as the primary key". This is generally true: the foreign key column’s data type should match the referenced primary key’s data type (and size/precision). Mismatched types would impede the integrity check and comparability.

Option 3: "the information being related must be the same as the primary key". Interpreting this as the foreign key value corresponding to a value in the parent table’s primary key is accurate; in a valid relationship, the foreign key must reference an existing primary (or candidate) key value.

Option 4: "it can have null or empty values". This is often permitted if the relationship is optional; a nullable foreign key means the row has no related parent row, which is allowed in many designs.

Option 5: "it must be the same field name as the primary key". This is not required; the foreign key column name on the child table does not need to match the parent table’s primary key column name. They can be named differently and still establish the relationship.

In summary, most textbooks and DBMS documentation emphasize that a foreign key references a candidate key in the parent (typically the primary key), must have a compatible data type, may be nullable if the relationship is optional, and does not have to share the same column name as the primary key. The statement in Option 1 asserts it must be a primary key in at least one table, which mischaracterizes the role of a foreign key and is therefore NOT true. The other options describe typical, valid properties or common allowances of foreign keys.

CSE 2111 AU2025 (10550) Carmen Quiz 9 - Chapter 10 - Database Concepts

Which of the following is NOT true about a foreign key that connects two tables in a database?

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