LEFT JOIN and RIGHT JOIN in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all customers and their orders, including customers without orders.

PostgreSQL

SELECT customers.name, orders.order_id FROM customers [1] orders ON customers.id = orders.customer_id;

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

ALEFT JOIN

BRIGHT JOIN

CINNER JOIN

DFULL JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN excludes customers without orders.

RIGHT JOIN would keep all orders, not customers.

LEFT JOIN returns all rows from the left table (customers) and matching rows from the right table (orders). Customers without orders still appear.

2fill in blank

medium

Complete the code to select all orders and their customers, including orders without customers.

PostgreSQL

SELECT orders.order_id, customers.name FROM orders [1] customers ON orders.customer_id = customers.id;

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

AFULL JOIN

BINNER JOIN

CLEFT JOIN

DRIGHT JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN excludes orders without customers.

Using LEFT JOIN would keep all orders, not customers.

RIGHT JOIN returns all rows from the right table (customers) and matching rows from the left table (orders). Orders without customers still appear.

3fill in blank

hard

Fix the error in the join to include all employees and their departments, even if some employees have no department.

PostgreSQL

SELECT employees.name, departments.dept_name FROM employees [1] departments ON employees.dept_id = departments.id;

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

AINNER JOIN

BLEFT JOIN

CRIGHT JOIN

DCROSS JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN excludes employees without departments.

RIGHT JOIN keeps all departments, not employees.

LEFT JOIN keeps all employees (left table) even if they have no matching department.

4fill in blank

hard

Fill both blanks to select all products and their suppliers, including products without suppliers.

PostgreSQL

SELECT products.name, suppliers.name FROM products [1] suppliers ON products.supplier_id [2] suppliers.id;

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

ALEFT JOIN

B=

C!=

DRIGHT JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using RIGHT JOIN would keep all suppliers, not products.

Using '!=' in ON condition is incorrect for matching.

LEFT JOIN keeps all products even if they have no supplier. The ON condition uses '=' to match supplier IDs.

5fill in blank

hard

Fill all three blanks to select all orders, their customers, and their shipping info, including orders without customers or shipping info.

PostgreSQL

SELECT orders.id, customers.name, shipping.address FROM orders [1] customers ON orders.customer_id [2] customers.id [3] JOIN shipping ON orders.shipping_id = shipping.id;

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

ALEFT JOIN

B=

CLEFT

DINNER

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN excludes orders without customers or shipping info.

Using '!=' in ON condition is incorrect.

LEFT JOIN keeps all orders even if no matching customer. The ON condition uses '='. The shipping table is joined with LEFT JOIN to keep orders without shipping info.