PostgreSQL: Intermediate SQL LEFT JOIN Exercises

This guide is specifically for PostgreSQL syntax.

Intermediate-level SQL LEFT JOIN practice exercises with solutions.

Exercise 1

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

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

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

Exercise 2

Question: Find customers who have never placed an order.

SELECT c.name
FROM customers c
LEFT JOIN orders o ON c.id = o.customer_id
WHERE o.id IS NULL;

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

PostgreSQL-Specific Notes

This page covers PostgreSQL syntax. Other databases may have different syntax for similar operations.