MySQL SQL
MySQL CASE
The MySQL CASE Statement
Similar to an if-then-else statement, the CASE statement 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
A sample from the Northwind sample database’s “OrderDetails” table is shown below:
| OrderDetailID | OrderID | ProductID | Quantity |
|---|---|---|---|
| 1 | 10248 | 11 | 12 |
| 2 | 10248 | 42 | 10 |
| 3 | 10248 | 72 | 5 |
| 4 | 10249 | 14 | 9 |
| 5 | 10249 | 51 | 40 |
MySQL 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 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);
