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 21

CASE Statements

If-else logic that lives inside your SQL.

IN THIS CHAPTER

CASE WHEN ... THEN ... END syntax
Using CASE to label and categorise rows
CASE inside aggregate functions — the pivot pattern

17.1 - Basic Case

Label employees by salary band

SELECT name, salary,
    CASE
        WHEN salary < 60000 THEN 'Junior'
        WHEN salary < 75000 THEN 'Mid-Level'
        ELSE 'Senior'
    END AS band
FROM employees ORDER BY salary;

17.2 - CASE in Aggregates (The Pivot Pattern)

Count by band in one row

SELECT
    SUM(CASE WHEN salary < 60000 THEN 1 ELSE 0 END) AS junior,
    SUM(CASE WHEN salary BETWEEN 60000 AND 74999 THEN 1 ELSE 0 END)
AS mid,
    SUM(CASE WHEN salary >= 75000 THEN 1 ELSE 0 END) AS senior
FROM employees;

✅ Interview Tip: This SUM(CASE WHEN ... END) pattern is the standard way to pivot rows into columns in SQL. It appears in almost every data analyst/data engineer interview. Know it cold.

Exercise 👇

Exercise:

Tasks

1.👉Classify employees as 'High' or 'Low' based on salary greater than 70000.

2.Classify employees as 'Tech' or 'Non-Tech' based on department.

3.Categorize employees into 'Low', 'Medium', and 'High' salary groups.

4.Show whether an employee has a manager or not.

5.Create a custom category: 'Top IT' for IT employees with salary > 70000, 'HR Team' for HR, and 'Other' for rest.

Stuck? Read this task's