SQL Case
The SQL CASE Expression
Similar to an if-then-else statement, the CASE expression iterates through conditions and returns a value when the first condition is satisfied. Thus, it will cease reading and return the result if a condition is true. It returns the result from the ELSE clause if none of the requirements are met.
It returns NULL if neither the conditions nor the ELSE portion are true.
CASE Syntax
CASE
WHEN condition1 THEN result1
WHEN condition2 THEN result2
WHEN conditionN THEN resultN
ELSE result
END;
Demo Database
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
When the first condition is satisfied, the following SQL loops through the conditions and produces a value:
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;
The clients will be arranged by City using the SQL below. But in the event that City is NULL, sort by Country:
Example
SELECT CustomerName, City, Country
FROM Customers
ORDER BY
(CASE
WHEN City IS NULL THEN Country
ELSE City
END);
