SQL Exercises

SQL LEFT JOIN Exercises (With Answers)

8 Exercises
~40 min
8 Intermediate

Exercise 1

intermediate

Question

List all employees and their departments, including employees without a department.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  department_id INT
);

CREATE TABLE departments (
  id INT PRIMARY KEY,
  name VARCHAR(100)
);
Show Solution

Solution

SQL
1SELECT e.name AS employee, d.name AS department
2FROM employees e
3LEFT JOIN departments d ON e.department_id = d.id;

Expected Output

| employee | department |
|---|---|
| John | Sales |
| Jane | NULL |

Explanation

LEFT JOIN returns all rows from the left table and matching rows from the right. Unmatched right-side rows show as NULL.

Exercise 1

intermediate

Question

List all employees and their departments, including employees without a department.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  department_id INT
);

CREATE TABLE departments (
  id INT PRIMARY KEY,
  name VARCHAR(100)
);
Show Solution

Solution

SQL
1SELECT e.name AS employee, d.name AS department
2FROM employees e
3LEFT JOIN departments d ON e.department_id = d.id;

Expected Output

| employee | department |
|---|---|
| John | Sales |
| Jane | NULL |

Explanation

LEFT JOIN returns all rows from the left table and matching rows from the right. Unmatched right-side rows show as NULL.

Exercise 1

intermediate

Question

List all employees and their departments, including employees without a department.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  department_id INT
);

CREATE TABLE departments (
  id INT PRIMARY KEY,
  name VARCHAR(100)
);
Show Solution

Solution

SQL
1SELECT e.name AS employee, d.name AS department
2FROM employees e
3LEFT JOIN departments d ON e.department_id = d.id;

Expected Output

| employee | department |
|---|---|
| John | Sales |
| Jane | NULL |

Explanation

LEFT JOIN returns all rows from the left table and matching rows from the right. Unmatched right-side rows show as NULL.

Exercise 1

intermediate

Question

List all employees and their departments, including employees without a department.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  department_id INT
);

CREATE TABLE departments (
  id INT PRIMARY KEY,
  name VARCHAR(100)
);
Show Solution

Solution

SQL
1SELECT e.name AS employee, d.name AS department
2FROM employees e
3LEFT JOIN departments d ON e.department_id = d.id;

Expected Output

| employee | department |
|---|---|
| John | Sales |
| Jane | NULL |

Explanation

LEFT JOIN returns all rows from the left table and matching rows from the right. Unmatched right-side rows show as NULL.

Exercise 2

intermediate

Question

Find customers who have never placed an order.

Table Schema

SQL
CREATE TABLE customers (id INT, name VARCHAR(100));
CREATE TABLE orders (id INT, customer_id INT, total DECIMAL);
Show Solution

Solution

SQL
1SELECT c.name
2FROM customers c
3LEFT JOIN orders o ON c.id = o.customer_id
4WHERE o.id IS NULL;

Expected Output

| name |
|---|
| Inactive Customer |

Explanation

This pattern (LEFT JOIN + WHERE IS NULL) finds rows in the left table that have no match in the right table.

Exercise 2

intermediate

Question

Find customers who have never placed an order.

Table Schema

SQL
CREATE TABLE customers (id INT, name VARCHAR(100));
CREATE TABLE orders (id INT, customer_id INT, total DECIMAL);
Show Solution

Solution

SQL
1SELECT c.name
2FROM customers c
3LEFT JOIN orders o ON c.id = o.customer_id
4WHERE o.id IS NULL;

Expected Output

| name |
|---|
| Inactive Customer |

Explanation

This pattern (LEFT JOIN + WHERE IS NULL) finds rows in the left table that have no match in the right table.

Exercise 2

intermediate

Question

Find customers who have never placed an order.

Table Schema

SQL
CREATE TABLE customers (id INT, name VARCHAR(100));
CREATE TABLE orders (id INT, customer_id INT, total DECIMAL);
Show Solution

Solution

SQL
1SELECT c.name
2FROM customers c
3LEFT JOIN orders o ON c.id = o.customer_id
4WHERE o.id IS NULL;

Expected Output

| name |
|---|
| Inactive Customer |

Explanation

This pattern (LEFT JOIN + WHERE IS NULL) finds rows in the left table that have no match in the right table.

Exercise 2

intermediate

Question

Find customers who have never placed an order.

Table Schema

SQL
CREATE TABLE customers (id INT, name VARCHAR(100));
CREATE TABLE orders (id INT, customer_id INT, total DECIMAL);
Show Solution

Solution

SQL
1SELECT c.name
2FROM customers c
3LEFT JOIN orders o ON c.id = o.customer_id
4WHERE o.id IS NULL;

Expected Output

| name |
|---|
| Inactive Customer |

Explanation

This pattern (LEFT JOIN + WHERE IS NULL) finds rows in the left table that have no match in the right table.

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