SQLCASE Expression
The SQL CASE Expression
TheCASE expression 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 theELSE clause.
If there is noELSE part and no conditions are true, it returns NULL.
CASE Syntax
CASE
WHENcondition1 THENresult1
WHENcondition2 THENresult2
WHENconditionN THENresultN
ELSEresult
END;
WHENcondition1 THENresult1
WHENcondition2 THENresult2
WHENconditionN THENresultN
ELSEresult
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
The following SQL goes through conditions 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;
Try it Yourself »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 following SQL will order the customers by City. However, if City is NULL, then order by Country:
Example
SELECT CustomerName, City, Country
FROM Customers
ORDER BY
(CASE
WHEN City IS NULL THEN Country
ELSE City
END);
Try it Yourself »FROM Customers
ORDER BY
(CASE
WHEN City IS NULL THEN Country
ELSE City
END);
