🚀 SQL Roadmap 2026 — Part 7

CASE Statements — Adding Business Logic to SQL 🧠

In the previous parts, you learned how to:

• Retrieve data with SELECT

• Filter data with WHERE

• Sort results with ORDER BY

• Summarize data with aggregate functions

• Group data with GROUP BY

Now it's time to learn how to make SQL think in business categories.

For example:

• Is this customer High Value, Medium Value, or Low Value?

• Is this employee's salary High, Medium, or Low?

• Is this order Small, Medium, or Large?

That's what the CASE expression helps you do.

1️⃣ What is CASE?

CASE allows you to create conditional logic inside SQL.

It's similar to:

• IF condition

• THEN result

• ELSE result

Basic Syntax

SELECT
    column_name,
    CASE
        WHEN condition THEN result
        WHEN condition THEN result
        ELSE result
    END AS new_column
FROM table_name;

2️⃣ Simple CASE Example

Suppose we have employee salaries.

We want to classify employees based on salary.

SELECT
    employee_name,
    salary,
    CASE
        WHEN salary >= 1000000 THEN 'High'
        WHEN salary >= 600000 THEN 'Medium'
        ELSE 'Low'
    END AS salary_category
FROM employees;

Result:

employee_name | salary  | salary_category
Rahul         | 1200000 | High
Priya         | 850000  | Medium
Amit          | 500000  | Low

3️⃣ How CASE Works

SQL checks conditions from top to bottom.

For:

CASE
    WHEN salary >= 1000000 THEN 'High'
    WHEN salary >= 600000 THEN 'Medium'
    ELSE 'Low'
END

SQL effectively asks:

• Is salary >= 1,000,000? YES → High

• NO → Is salary >= 600,000? YES → Medium

• NO → Low

Once a matching WHEN condition is found, SQL returns that result.

4️⃣ Order of WHEN Conditions Matters

Consider:

CASE
    WHEN salary >= 600000 THEN 'Medium'
    WHEN salary >= 1000000 THEN 'High'
    ELSE 'Low'
END

This is problematic.

Why?

Someone earning ₹12 lakh satisfies:

• salary >= 600000 first.

So SQL labels them:

• Medium instead of High

Better:

CASE
    WHEN salary >= 1000000 THEN 'High'
    WHEN salary >= 600000 THEN 'Medium'
    ELSE 'Low'
END

Rule:

• Put more specific or higher-priority conditions before broader conditions.

5️⃣ CASE With Text Conditions

You can also classify based on text.

Example:

SELECT
    employee_name,
    department,
    CASE
        WHEN department = 'IT' THEN 'Technology'
        WHEN department = 'Finance' THEN 'Corporate'
        WHEN department = 'HR' THEN 'Corporate'
        ELSE 'Other'
    END AS department_group
FROM employees;

6️⃣ CASE With Multiple Conditions

You can use AND and OR inside WHEN.

Example:

SELECT
    customer_name,
    city,
    customer_segment,
    CASE
        WHEN customer_segment = 'Premium'
             AND city = 'Mumbai'
        THEN 'Premium Mumbai'

        WHEN customer_segment = 'Premium'
        THEN 'Other Premium'

        ELSE 'Standard'
    END AS customer_group
FROM customers;

7️⃣ CASE With IN

You can combine CASE with IN.

SELECT
    customer_name,
    city,
    CASE
        WHEN city IN ('Mumbai', 'Pune', 'Nashik')
            THEN 'Maharashtra'
        WHEN city IN ('Delhi', 'Noida', 'Gurgaon')
            THEN 'NCR'
        ELSE 'Other'
    END AS region
FROM customers;

This is useful for creating business regions.

8️⃣ CASE With BETWEEN

Example: