PostgreSQL: Intermediate SQL GROUP BY Exercises

This guide is specifically for PostgreSQL syntax.

Intermediate-level SQL GROUP BY practice exercises with solutions.

Exercise 1

Question: Count the number of employees in each department.

SELECT department, COUNT(*) AS employee_count
FROM employees
GROUP BY department;

GROUP BY groups rows by one or more columns. Aggregate functions like COUNT operate on each group.

Exercise 2

Question: Calculate the average salary by department, ordered highest to lowest.

SELECT department, AVG(salary) AS avg_salary
FROM employees
GROUP BY department
ORDER BY avg_salary DESC;

You can use column aliases in ORDER BY. The query calculates average salary per department.

PostgreSQL-Specific Notes

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