SQL CASE

The SQL CASE Expression

The CASE expression evaluates conditions sequentially and returns a value once the first condition is met, akin to an if-then-else statement. If none of the conditions are true, it returns the value specified in the ELSE clause.

In the absence of an ELSE clause, and if no conditions are met, it returns NULL.

CASE Syntax

CASE
    WHEN condition1 THEN result1
    WHEN condition2 THEN result2
    WHEN conditionN THEN resultN
    ELSE result
END;

Demo Database

Here is an excerpt from the “OrderDetails” table within the Northwind sample database:

OrderDetailID	OrderID	ProductID	Quantity
1	10248	11	12
2	10248	42	10
3	10248	72	5
4	10249	14	9
5	10249	51	40

SQL CASE Examples

The following SQL statement evaluates conditions sequentially and returns a value when the first condition is met.

Example

SELECT OrderID, Quantity,
CASE
    WHEN Quantity > 30 THEN ‘The quantity is greater than 30’
    WHEN Quantity = 30 THEN ‘The quantity is 30’
    ELSE ‘The quantity is under 30’
END AS QuantityText
FROM OrderDetails;

This SQL statement will arrange the customers by City. In case the City is NULL, it will sort by Country instead.

Example

SELECT CustomerName, City, Country
FROM Customers
ORDER BY
(CASE
WHEN City IS NULL THEN Country
ELSE City
END);