Data Science & Machine Learnin… on Telegram: “🚀 Data Science Roadmap 2026 📍 Phase 3: SQL for…”

🚀 Data Science Roadmap 2026

📍 Phase 3: SQL for Data Science

📖 Topic 7 — HAVING

HAVING is used to filter grouped results.

The most important thing to remember:

WHERE → filters rows

HAVING → filters groups

🔹 Why Do We Need HAVING?

Suppose you want to find departments that have more than 5 employees.

First, you need to group employees by department:

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

But if you want only departments with more than 5 employees, use HAVING:

SELECT department, COUNT(*) AS employee_count
FROM employees
GROUP BY department
HAVING COUNT(*) > 5;

The grouping happens first, and then HAVING filters the groups.

🔹 Basic Syntax

SELECT column_name, aggregate_function(column_name)
FROM table_name
GROUP BY column_name
HAVING condition;

🔹 HAVING with COUNT()

Find departments having more than 10 employees:

SELECT department, COUNT(*) AS employee_count
FROM employees
GROUP BY department
HAVING COUNT(*) > 10;

🔹 HAVING with SUM()

Find regions where total sales exceed 100000:

SELECT region, SUM(sales) AS total_sales
FROM sales
GROUP BY region
HAVING SUM(sales) > 100000;

🔹 HAVING with AVG()

Find departments where the average salary is greater than 70000:

SELECT department, AVG(salary) AS avg_salary
FROM employees
GROUP BY department
HAVING AVG(salary) > 70000;

🔹 HAVING with MAX()

Find departments where the highest salary is greater than 150000:

SELECT department, MAX(salary) AS highest_salary
FROM employees
GROUP BY department
HAVING MAX(salary) > 150000;

🔹 WHERE vs HAVING

This is one of the most frequently asked SQL interview questions.

WHERE Filters individual rows.

SELECT *
FROM employees
WHERE salary > 50000;

It removes individual records that don't meet the condition.

HAVING

Filters groups after GROUP BY.

SELECT department, AVG(salary) AS avg_salary
FROM employees
GROUP BY department
HAVING AVG(salary) > 70000;

It removes entire groups that don't meet the condition.

🔹 Using WHERE and HAVING Together

You can use both.

Suppose you want departments where:

• Only employees earning more than 50000 are considered

• The department must have at least 5 such employees

SELECT department, COUNT(*) AS employee_count
FROM employees
WHERE salary > 50000
GROUP BY department
HAVING COUNT(*) >= 5;

Conceptually:

All employees
     ↓
WHERE
     ↓
Employees with salary > 50000
     ↓
GROUP BY
     ↓
Create department groups
     ↓
HAVING
     ↓
Keep groups with at least 5 employees

🔹 HAVING with ORDER BY

You can also sort the filtered groups.

SELECT department, SUM(salary) AS total_salary
FROM employees
GROUP BY department
HAVING SUM(salary) > 500000
ORDER BY total_salary DESC;

This finds departments whose total salary exceeds 500000 and displays the highest totals first.

🔹 HAVING Without GROUP BY

Some SQL databases allow HAVING without an explicit GROUP BY, treating the entire result as a single group.

For example:

SELECT COUNT(*) AS employee_count
FROM employees
HAVING COUNT(*) > 100;

This returns the result only if there are more than 100 employees.

For beginners, however, focus primarily on the common pattern:

GROUP BY → HAVING

🔹 Common Mistake

❌ Incorrect:

SELECT department, COUNT(*)
FROM employees
WHERE COUNT(*) > 5
GROUP BY department;