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SQL CASE 关键字


CASE

CASE命令用于根据条件创建不同的输出。

以下SQL经历了几个条件,并在满足指定条件时返回一个值:

实例

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;

运行实例»

以下SQL将按City排序。但是,如果City为NULL,则按Country排序:

实例

SELECT CustomerName, City, Country
FROM Customers
ORDER BY
(CASE
    WHEN City IS NULL THEN Country
    ELSE City
END);

运行实例»