SQL CASE 关键字
CASE
The CASE command is used is to create different output based on conditions.
The following SQL goes through several conditions and returns a value when the specified condition is met
示例
SELECT OrderID, Quantity,
CASE
WHEN Quantity > 30 THEN '数量大于 30'
WHEN Quantity = 30 THEN '数量等于 30'
ELSE '数量小于 30'
END
FROM OrderDetails;
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以下 SQL 语句将按城市对客户进行排序。但是，如果城市为 NULL，则按国家排序
示例
SELECT CustomerName, City, Country
FROM Customers
ORDER BY
(CASE
WHEN City IS NULL THEN Country
ELSE City
END);
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