In a nutshell
The MySQL CASE expression is used to evaluate conditions and return a result based on the result of those conditions. The CASE expression can take two forms: simple and searched.
1. Simple CASE expression
CASE expression WHEN value1 THEN result1 WHEN value2 THEN result2 ... ELSE default_result END
SELECT id, name, CASE department WHEN 'IT' THEN 'Information Technology' WHEN 'HR' THEN 'Human Resources' WHEN 'FIN' THEN 'Finance' ELSE 'Unknown' END AS department_name FROM employees;
2. Searched CASE expression
CASE WHEN condition1 THEN result1 WHEN condition2 THEN result2 ... ELSE default_result END
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;