SQL CASE Syntax
CASE case_value WHEN when_value THEN statement_list [WHEN when_value THEN statement_list] ... [ELSE statement_list] END CASE
CASE 搜索条件
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 FROM OrderDetails;
CASE分组条件
SELECT CustomerName, City, Country FROM Customers ORDER BY (CASE WHEN City IS NULL THEN Country ELSE City END);