The SQL CASE Statement
The CASE statement goes through conditions and returns a value when the first condition is met (like an IF-THEN-ELSE statement). So, once a condition is true, it will stop reading and return the result. If no conditions are true, it returns the value in the ELSE clause.
If there is no ELSE part and no conditions are true, it returns NULL.
WHEN condition1 THEN result1
WHEN condition2 THEN result2
WHEN conditionN THEN resultN
Below is a selection from the "OrderDetails" table in 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 goes through conditions and returns a value when the first condition is met:
SELECT OrderID, Quantity,
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