LEFT JOIN with NULL result rows in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all customers and their orders, including customers with no orders.

SQL

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.

Using RIGHT JOIN or FULL JOIN changes which rows are included.

The LEFT JOIN returns all rows from the left table (customers) and matching rows from the right table (orders). If there is no match, order columns will be NULL.

2fill in blank

medium

Complete the code to find customers with no orders using LEFT JOIN.

SQL

SELECT customers.name FROM customers LEFT JOIN orders ON customers.id = orders.customer_id WHERE orders.order_id [1];

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

AIS NOT NULL

BIS NULL

C= 0

D<> NULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using = NULL or <> NULL which are invalid in SQL.

Using IS NOT NULL which finds customers with orders.

When using LEFT JOIN, customers without orders have orders.order_id as NULL. Filtering with IS NULL finds those customers.

3fill in blank

hard

Fix the error in the query to include all customers and their orders, showing NULL for missing orders.

SQL

SELECT c.name, o.order_id FROM customers c [1] orders o ON c.id = o.customer_id WHERE o.order_id > 100;

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

ARIGHT JOIN

BINNER JOIN

CLEFT JOIN

DFULL JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN excludes customers without orders.

Filtering on right table columns in WHERE removes NULL rows.

Using LEFT JOIN keeps all customers. But the WHERE clause filters out NULL orders, so to keep NULLs, the condition should be in the ON clause or use LEFT JOIN with care.

4fill in blank

hard

Fill both blanks to select all customers and their orders, showing NULL for missing orders, and order by customer name.

SQL

SELECT [1], [2] FROM customers LEFT JOIN orders ON customers.id = orders.customer_id ORDER BY customers.name;

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

Acustomers.name

Borders.order_id

Ccustomers.id

Dorders.customer_id

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting wrong columns like IDs that don't show meaningful info.

Not ordering by customer name as requested.

Selecting customers.name and orders.order_id shows customer names and their orders. LEFT JOIN ensures all customers appear, even without orders (NULL order_id).

5fill in blank

hard

Fill all three blanks to create a query that lists all customers, their order IDs, and filters to show only customers with no orders.

SQL

SELECT [1], [2] FROM customers [3] orders ON customers.id = orders.customer_id WHERE orders.order_id IS NULL;

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

Acustomers.name

Borders.order_id

CLEFT JOIN

DINNER JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN excludes customers without orders.

Not checking for NULL order_id to find customers without orders.

This query uses LEFT JOIN to include all customers, selects customer names and order IDs, and filters for customers with no orders by checking orders.order_id IS NULL.