A CASE expression evaluates conditions and returns different values based on those conditions. When combined with JOINs, it can classify or transform related data from multiple tables.
Business reports often require classifications such as High, Medium, Low, Active, Inactive, or Risk categories after combining information from multiple tables.
Join customers with their orders and classify customers based on their total order amount.
SELECT
c.CustomerName,
o.OrderAmount,
CASE
WHEN o.OrderAmount >= 100000 THEN 'High'
WHEN o.OrderAmount >= 50000 THEN 'Medium'
ELSE 'Low'
END AS OrderCategory
FROM Customers c
INNER JOIN Orders o
ON c.CustomerID = o.CustomerID;Used in customer segmentation, financial reporting, risk analysis, sales reporting, and business dashboards.
- CASE can be used inside JOIN-based queries.
- CASE creates business classifications.
- Conditions can use columns from joined tables.
- Multiple conditions can be evaluated.
- CASE is useful for reporting logic.
Can CASE be used with JOIN?
Yes. CASE can evaluate columns from one or more joined tables and return calculated classifications.
Why use CASE after joining tables?
It allows business rules and classifications to be applied to the combined data.