CASE

The CASE command is employed to generate various outputs based on different conditions. The provided SQL evaluates multiple conditions and returns a value when a specified condition is satisfied.

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
FROM OrderDetails;

The following SQL statement arranges customers by their city. However, if the city field is NULL, it will instead order them by country.

Example

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