Foreign key ON DELETE behavior in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify that deleting a parent row will delete matching child rows.

SQL

CREATE TABLE orders (
  order_id INT PRIMARY KEY,
  customer_id INT,
  FOREIGN KEY (customer_id) REFERENCES customers(customer_id) ON DELETE [1]
);

Drag options to blanks, or click blank then click option'

ACASCADE

BRESTRICT

CSET NULL

DNO ACTION

Attempts:

3 left

💡 Hint

Common Mistakes

Using RESTRICT which prevents deletion if child rows exist.

Using SET NULL without allowing NULL in the foreign key column.

The CASCADE option deletes child rows when the parent row is deleted.

2fill in blank

medium

Complete the code to prevent deletion of a parent row if child rows exist.

SQL

ALTER TABLE orders
ADD CONSTRAINT fk_customer FOREIGN KEY (customer_id) REFERENCES customers(customer_id) ON DELETE [1];

Drag options to blanks, or click blank then click option'

ARESTRICT

BCASCADE

CSET NULL

DNO ACTION

Attempts:

3 left

💡 Hint

Common Mistakes

Using CASCADE which deletes child rows automatically.

Confusing NO ACTION with RESTRICT (they behave similarly but differ in timing).

The RESTRICT option prevents deleting a parent row if child rows exist.

3fill in blank

hard

Fix the error in the foreign key definition to set the child foreign key to NULL when the parent is deleted.

SQL

CREATE TABLE orders (
  order_id INT PRIMARY KEY,
  customer_id INT,
  FOREIGN KEY (customer_id) REFERENCES customers(customer_id) ON DELETE [1]
);

Drag options to blanks, or click blank then click option'

ACASCADE

BRESTRICT

CSET NULL

DNO ACTION

Attempts:

3 left

💡 Hint

Common Mistakes

Using CASCADE which deletes child rows instead of setting NULL.

Using RESTRICT which prevents deletion of the parent row.

The SET NULL option sets the foreign key column to NULL when the parent row is deleted.

4fill in blank

hard

Fill both blanks to create a foreign key that prevents deletion and updates child keys on parent update.

SQL

CREATE TABLE orders (
  order_id INT PRIMARY KEY,
  customer_id INT,
  FOREIGN KEY (customer_id) REFERENCES customers(customer_id) ON DELETE [1] ON UPDATE [2]
);

Drag options to blanks, or click blank then click option'

ARESTRICT

BCASCADE

CSET NULL

DNO ACTION

Attempts:

3 left

💡 Hint

Common Mistakes

Using CASCADE for ON DELETE which deletes child rows.

Using NO ACTION which may defer enforcement.

RESTRICT prevents deleting a parent row if child rows exist, and CASCADE updates child foreign keys when the parent key changes.

5fill in blank

hard

Fill all three blanks to create a foreign key that sets child keys to NULL on delete, cascades updates, and restricts deletes on another key.

SQL

CREATE TABLE orders (
  order_id INT PRIMARY KEY,
  customer_id INT,
  product_id INT,
  FOREIGN KEY (customer_id) REFERENCES customers(customer_id) ON DELETE [1] ON UPDATE [2],
  FOREIGN KEY (product_id) REFERENCES products(product_id) ON DELETE [3]
);

Drag options to blanks, or click blank then click option'

ASET NULL

BCASCADE

CRESTRICT

DNO ACTION

Attempts:

3 left

💡 Hint

Common Mistakes

Using CASCADE for delete on product_id which deletes child rows.

Using NO ACTION which may not enforce immediate constraints.

The first foreign key sets child keys to NULL on delete (SET NULL) and cascades updates (CASCADE). The second foreign key restricts deletion (RESTRICT).