FOREIGN KEY constraint in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a foreign key constraint linking the orders table to the customers table.

SQL

CREATE TABLE orders (
  order_id INT PRIMARY KEY,
  customer_id INT,
  CONSTRAINT fk_customer FOREIGN KEY (customer_id) REFERENCES [1](customer_id)
);

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

Aemployees

Bproducts

Corders

Dcustomers

Attempts:

3 left

💡 Hint

Common Mistakes

Referencing the wrong table name in the foreign key constraint.

Using the same table name as the current table.

The foreign key in orders references the customer_id in the customers table to ensure data integrity.

2fill in blank

medium

Complete the code to add a foreign key constraint to the payments table referencing the orders table.

SQL

ALTER TABLE payments
ADD CONSTRAINT fk_order FOREIGN KEY (order_id) REFERENCES [1](order_id);

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

Aorders

Bcustomers

Cpayments

Dinvoices

Attempts:

3 left

💡 Hint

Common Mistakes

Referencing the wrong table in the foreign key.

Trying to reference the same table being altered.

The foreign key order_id in payments must reference the order_id in the orders table.

3fill in blank

hard

Fix the error in the foreign key constraint definition by completing the code.

SQL

CREATE TABLE order_items (
  item_id INT PRIMARY KEY,
  order_id INT,
  CONSTRAINT fk_order FOREIGN KEY (order_id) REFERENCES [1](order_id)
);

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

Aorders

Bcustomers

Citems

Dorder_items

Attempts:

3 left

💡 Hint

Common Mistakes

Referencing the same table in the foreign key constraint.

Referencing an unrelated table.

The foreign key order_id in order_items must reference the order_id in the orders table, not itself or unrelated tables.

4fill in blank

hard

Fill both blanks to create a foreign key constraint with cascading delete from employees to departments.

SQL

CREATE TABLE employees (
  emp_id INT PRIMARY KEY,
  dept_id INT,
  CONSTRAINT fk_dept FOREIGN KEY ([1]) REFERENCES departments([2]) ON DELETE CASCADE
);

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

Adept_id

Bemp_id

Cdepartment_id

Demployee_id

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping foreign key and referenced key columns.

Using incorrect column names.

The foreign key column in employees is dept_id, which references department_id in departments. The ON DELETE CASCADE ensures related employees are deleted if a department is removed.

5fill in blank

hard

Fill all three blanks to create a foreign key constraint on enrollments referencing students with cascading update and delete.

SQL

CREATE TABLE enrollments (
  enrollment_id INT PRIMARY KEY,
  student_id INT,
  CONSTRAINT fk_student FOREIGN KEY ([1]) REFERENCES [2]([3]) ON UPDATE CASCADE ON DELETE CASCADE
);

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

Astudent_id

Bstudents

Denrollments

Attempts:

3 left

💡 Hint

Common Mistakes

Referencing the wrong table or column.

Forgetting to match foreign key and referenced column names.

The foreign key student_id in enrollments references student_id in the students table. Cascading update and delete keep data consistent when student records change or are removed.