When working with SQL databases, sometimes we need to apply conditional case when sql logic within queries. This is where the CASE WHEN statement becomes useful. It works like an if-else condition, allowing you to return different values based on specific conditions.
Why Use CASE WHEN?
The CASE WHEN statement is used in SQL for:
- Data transformation – Converting raw data into meaningful values.
- Categorization – Grouping data based on specific conditions.
- Conditional calculations – Applying different formulas depending on conditions.
Syntax of CASE WHEN
The basic structure of CASE WHEN is:
sqlCopyEditCASE
WHEN condition_1 THEN result_1
WHEN condition_2 THEN result_2
ELSE default_result
END
Types of CASE WHEN
There are two types:
- Simple CASE – Compares a single value to multiple options.
- Searched CASE – Uses different conditions for each case.
Real-World Example with Data Table
Consider a sales database where we categorize employees based on sales performance.
Employee Sales Table Before CASE WHEN
| Employee | Sales |
|---|---|
| John | 5000 |
| Sarah | 12000 |
| Mike | 8000 |
| Emma | 15000 |
| David | 4000 |
Now, we categorize employees into “High,” “Medium,” or “Low” performers.
Employee Sales Table After CASE WHEN
| Employee | Sales | Performance Category |
|---|---|---|
| John | 5000 | Medium |
| Sarah | 12000 | High |
| Mike | 8000 | Medium |
| Emma | 15000 | High |
| David | 4000 | Low |
Use Cases of CASE WHEN in SQL
- Data Reporting: Convert numeric values into user-friendly text.
- Calculating Discounts: Apply discounts based on purchase amount.
- Customer Segmentation: Classify users into different tiers.
Best Practices for Using CASE WHEN
✅ Keep conditions simple and clear.
✅ Always include an ELSE statement for unexpected values.
✅ Optimize performance by avoiding complex logic in large datasets.
Final Thoughts
The CASE WHEN statement in SQL is a powerful tool for implementing conditional logic. Whether you’re working with financial reports, customer segmentation, or sales data, mastering CASE WHEN will improve your SQL queries significantly.
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