LEFT JOIN execution behavior in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all records from the left table and matching records from the right table.

SQL

SELECT * FROM employees LEFT JOIN departments ON employees.department_id [1] departments.id;

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

A>

B!=

C=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '=' causes no matches.

Using '>' or '<' does not correctly join related rows.

The LEFT JOIN requires an equality condition to match rows from the left and right tables.

2fill in blank

medium

Complete the code to count employees without a department.

SQL

SELECT COUNT(*) FROM employees LEFT JOIN departments ON employees.department_id = departments.id WHERE departments.id [1] NULL;

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

A=

BIS

CLIKE

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '= NULL' which always returns false.

Using 'LIKE NULL' which is invalid.

To check for NULL values in SQL, use 'IS NULL' instead of '= NULL'.

3fill in blank

hard

Fix the error in the LEFT JOIN query to correctly show all customers and their orders.

SQL

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

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

ALEFT

BRIGHT

CFULL

DINNER

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN excludes customers without orders.

RIGHT JOIN reverses the table order.

FULL JOIN includes unmatched rows from both tables.

LEFT JOIN returns all rows from the left table (customers) and matching rows from orders.

4fill in blank

hard

Fill both blanks to create a LEFT JOIN that shows all products and their sales, including products with no sales.

SQL

SELECT products.name, sales.amount FROM products [1] JOIN sales ON products.id [2] sales.product_id;

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

ALEFT

BRIGHT

C=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using RIGHT JOIN excludes products without sales.

Using '!=' in ON clause causes incorrect matches.

LEFT JOIN keeps all products, and '=' matches product IDs to sales.

5fill in blank

hard

Fill all three blanks to write a LEFT JOIN query that lists students with grades above 80.

SQL

SELECT students.name, grades.score FROM students [1] JOIN grades ON students.id [2] grades.student_id WHERE grades.score [3] 80;

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

ALEFT

B=

C>

DINNER

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN (D) instead of the required LEFT JOIN.

Using '<' or '=' instead of '>' in the WHERE clause.

Using '!=' in ON clause causes wrong matches.

LEFT JOIN, '=' matches IDs, and '> 80' filters grades above 80. Note the WHERE clause filters out non-matching rows.