SQL GROUP BY & HAVING Explained with Examples + Practice Questions

When to Use GROUP BY & HAVING

• Use GROUP BY to group rows based on a column
• Use HAVING to filter grouped results

These are essential for:

• Data analysis
• Reporting
• SQL interviews (very high frequency)

Example Dataset

Table: employees

GROUP BY

GROUP BY groups rows that have the same values in a column.

Example: Count employees per department

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

Example: Average salary per department

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

Important Rule

Every column in SELECT must be:

• Either in GROUP BY
• Or used with an aggregate function

HAVING

HAVING is used to filter grouped results.

Example: Departments with more than 2 employees

sql
SELECT department, COUNT(*) AS total
FROM employees
GROUP BY department
HAVING COUNT(*) > 2;

WHERE vs HAVING

Example Combining WHERE and HAVING

sql
SELECT department, AVG(salary) AS avg_salary
FROM employees
WHERE salary > 40000
GROUP BY department
HAVING AVG(salary) > 50000;

GROUP BY + ORDER BY

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

Key Concepts

• GROUP BY groups data
• HAVING filters grouped data
• WHERE filters before grouping
• Always use aggregate functions with GROUP BY
• Common interview pattern

GROUP BY vs HAVING Summary

Common Questions (FAQ)

What is GROUP BY in SQL

GROUP BY groups rows with the same values and applies aggregate functions.

What is HAVING in SQL

HAVING filters grouped results after aggregation.

Difference between WHERE and HAVING

WHERE filters rows before grouping, HAVING filters after grouping.

Can we use HAVING without GROUP BY

Yes, but it is uncommon and usually not needed.

Internal Learning Links

• Learn Aggregations
• Learn WHERE filtering
• Learn ORDER BY

Practice CTA

Practice GROUP BY and HAVING problems on Schoolabe to master interview-level SQL queries.