DataBolt

All Lessons

Introduction to SQL

SQL Lesson 1: Your Sample Database

SQL Lesson 2: SELECT — Reading data

SQL Lesson 3: WHERE — Filtering rows

SQL Lesson 4: AND, OR, NOT

SQL Lesson 5: BETWEEN, IN, LIKE

SQL Lesson 6: NULL — The Mystery Value

SQL Lesson 7: ORDER BY

SQL Lesson 8: LIMIT & OFFSET

SQL Lesson 9: Aggregate Functions

SQL Lesson 10: GROUP BY

SQL Lesson 11: HAVING

SQL Lesson 12: INNER JOINs

SQL Lesson 13: LEFT JOINs

SQL Lesson 14: RIGHT JOINs

SQL Lesson 15: SELF JOINs

SQL Lesson 16: UNION JOINs

SQL Lesson 17: Joining Multiple Tables

SQL Lesson 18: Subqueries

SQL Lesson 19: CTEs (WITH)

SQL Lesson 20: CASE Statements

SQL Lesson 21: Window Functions

SQL Lesson 22: String Functions

SQL Lesson 23: Date & Time Functions

SQL Lesson 24: INSERT, UPDATE, DELETE

SQL Lesson 25: CREATE TABLE & DDL

SQL Lesson 26: Indexes & Performance

SQL Lesson 27: Transactions & ACID

SQL Lesson 28: SQL Execution Order

SQL Lesson 29: 50 Practice Problems

CHAPTER 11

GROUP BY

Aggregating by category — the analytics workhorse.

IN THIS CHAPTER

How GROUP BY splits data into buckets before aggregating
Grouping by a single column
Grouping by multiple columns
Combining GROUP BY with WHERE

🌟 Think of it this way: GROUP BY is like sorting coins into labelled bags — all 1-rupee coins into one bag, all 5-rupee into another — and then counting each bag separately. Each bag becomes one row in your result.

11.1 - Employees Department

SQL

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

Exercise 👇

Exercise:

Tasks

1.👉Find the number of employees in each department.

2.Find the total salary of each department.

3.Find the average salary of each department.

4.Find the minimum and maximum salary in each department.

Stuck? Read this task's