Learn Nested and Multiple Conditions | CASE WHEN for Business Logic

When you need to capture complex business logic in your queries, using multiple and nested CASE WHEN statements is essential. These techniques allow you to create sophisticated categorizations and decision trees that mirror real-world scenarios, such as customer segmentation or targeted business actions. By combining and layering conditions, you can transform raw data into actionable insights directly within your SQL queries.


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SELECT order_id,
       CASE
           WHEN total_amount > 200 THEN 'VIP'
           WHEN total_amount > 100 THEN 'High'
           ELSE 'Standard'
       END AS order_tier
FROM orders;

This query demonstrates how to build tiered logic for customer segmentation. By evaluating the total_amount column in descending order of value, each order is classified as "VIP," "High," or "Standard." The first condition met determines the result, so the order of conditions is crucial for correct categorization.


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SELECT r.region_name,
       CASE
           WHEN r.region_name = 'North America' AND o.total_amount > 150 THEN 'Priority'
           ELSE 'Regular'
       END AS region_priority
FROM orders o
JOIN regions r ON o.region_id = r.region_id;

Combining multiple conditions in a single CASE WHEN clause allows you to target specific business actions. In this updated query, you join the orders table with the regions table to access the region_name column. Only orders from the "North America" region with a total_amount greater than 150 are marked as "Priority". All other orders are labeled as "Regular". This approach helps you focus on high-value opportunities or risks within specific regions.

Definition

A nested CASE WHEN statement is a CASE expression placed inside another CASE expression. This structure enables multi-level decision making, where the outcome of one condition leads to another set of conditions being evaluated. Nested logic is useful when your business rules depend on more than one layer of criteria.

To keep your CASE WHEN statements readable and maintainable, always:

Use clear and descriptive labels for each outcome;
Keep the logic as simple as possible by breaking up complex rules into smaller steps;
Indent and format your code for clarity, especially when nesting CASE statements;
Add comments when logic is non-obvious to future readers.

Applying these tips will help you and your team maintain complex business logic in SQL queries with confidence and ease.

1. How can you create multiple categories using CASE WHEN?

2. What is the benefit of nesting CASE WHEN statements?

3. Give an example of combining two conditions in a CASE WHEN clause.

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              1234567
            
SELECT order_id,
       CASE
           WHEN total_amount > 200 THEN 'VIP'
           WHEN total_amount > 100 THEN 'High'
           ELSE 'Standard'
       END AS order_tier
FROM orders;


              1234567
            
SELECT r.region_name,
       CASE
           WHEN r.region_name = 'North America' AND o.total_amount > 150 THEN 'Priority'
           ELSE 'Regular'
       END AS region_priority
FROM orders o
JOIN regions r ON o.region_id = r.region_id;