Which of the following statements about the FOREIGN KEY constraint is incorrect?

Question

Which of the following statements about the FOREIGN KEY constraint is incorrect?​

BlackTom AI · Accepted Answer

Question restatement: Which of the following statements about the FOREIGN KEY constraint is incorrect?

Option 1: 'The constraint is added to (or defined in) the child table to ensure the referential integrity between the parent table and the child table.' This is a correct description. A foreign key is defined on the child (referencing) table and enforces that values in the foreign key column(s) correspond to existing values in the parent table, thus maintaining referential integrity.

Option 2: 'When the constraint exists, by default a record cannot be deleted from the parent table if matching entries exist in the child table.' This statement is also correct in many database systems. Unless you specify a cascading action (like ON DELETE CASCADE) or other options (like SET NULL, NO ACTION), deleting a parent row that has dependent child rows would be blocked or rejected to preserve referential integrity.

Option 3: 'When the keywords ON DELETE CASCADE are included in the constraint, the Foreign Key constraint will be dropped when you drop a Primary Key constraint of the parent table.' This is the incorrect statement. ON DELETE CASCADE defines behavior for what happens to child rows when a parent row is deleted, not what happens to the FK constraint itself when the parent’s primary key is dropped. Dropping a primary key typically affects the key’s existence and may require dropping or altering dependent foreign keys, but it does not entail automatically dropping the entire foreign key constraint simply because ON DELETE CASCADE was specified. The constraint’s existence and behavior are not tied to the act of dropping a primary key in this way.

Option 4: 'When the keywords ON DELETE CASCADE are included in the constraint, a corresponding child record will be automatically removed when the parent record is deleted.' This is a correct description of ON DELETE CASCADE. Deleting a parent row cascades the delete to all matching child rows, removing them automatically.

Summary of reasoning: Options 1, 2, and 4 accurately describe standard foreign key behavior in relational databases. Option 3 misstates the effect of ON DELETE CASCADE on the FK constraint itself when the parent table’s primary key is dropped, which is not how cascading delete semantics work. The incorrectness lies in conflating cascade delete behavior with automatic dropping of the constraint during a primary key drop.

Which of the following statements about the FOREIGN KEY constraint is incorrect?Single choice

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Which of the following statements about the FOREIGN KEY constraint is incorrect?​Single choice

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