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SQL Server中Case语句的不同用法
来源: 互联网 发布时间：2014-08-29
本文导语: 本节内容： SQL Server中Case语句的用法举例。 首先，CASE 的语法。 在一般的 SELECT 中，其语法如下： SELECT = CASE WHEN THEN WHEN THEN ELSE END 以上代码需用具体的参数代替尖括号中的内容。 例子： 代码示例: USE pubs G...
本节内容：
SQL Server中Case语句的用法举例。
首先，CASE 的语法。
在一般的 SELECT 中，其语法如下：
以上代码需用具体的参数代替尖括号中的内容。
例子：
代码示例:
USE pubs
GO
SELECT
Title,
'Price Range' =
CASE
WHEN price IS NULL THEN 'Unpriced'
WHEN price < 10 THEN 'Bargain'
WHEN price BETWEEN 10 and 20 THEN 'Average'
ELSE 'Gift to impress relatives'
END
FROM titles
ORDER BY price
GO
GO
SELECT
Title,
'Price Range' =
CASE
WHEN price IS NULL THEN 'Unpriced'
WHEN price < 10 THEN 'Bargain'
WHEN price BETWEEN 10 and 20 THEN 'Average'
ELSE 'Gift to impress relatives'
END
FROM titles
ORDER BY price
GO
代码说明：CASE 的典型用法，但是使用 CASE 其实可以做更多的事情。
比方说下面的 GROUP BY 子句中的 CASE：
代码示例:
SELECT 'Number of Titles', Count(*)
FROM titles
GROUP BY
CASE
WHEN price IS NULL THEN 'Unpriced'
WHEN price < 10 THEN 'Bargain'
WHEN price BETWEEN 10 and 20 THEN 'Average'
ELSE 'Gift to impress relatives'
END
GO
FROM titles
GROUP BY
CASE
WHEN price IS NULL THEN 'Unpriced'
WHEN price < 10 THEN 'Bargain'
WHEN price BETWEEN 10 and 20 THEN 'Average'
ELSE 'Gift to impress relatives'
END
GO
还可以组合这些选项，添加一个 ORDER BY 子句，如下所示：
代码示例:
USE pubs
GO
SELECT
CASE
WHEN price IS NULL THEN 'Unpriced'
WHEN price < 10 THEN 'Bargain'
WHEN price BETWEEN 10 and 20 THEN 'Average'
ELSE 'Gift to impress relatives'
END AS Range,
Title
FROM titles
GROUP BY
CASE
WHEN price IS NULL THEN 'Unpriced'
WHEN price < 10 THEN 'Bargain'
WHEN price BETWEEN 10 and 20 THEN 'Average'
ELSE 'Gift to impress relatives'
END,
Title
ORDER BY
CASE
WHEN price IS NULL THEN 'Unpriced'
WHEN price < 10 THEN 'Bargain'
WHEN price BETWEEN 10 and 20 THEN 'Average'
ELSE 'Gift to impress relatives'
END,
Title
GO
GO
SELECT
CASE
WHEN price IS NULL THEN 'Unpriced'
WHEN price < 10 THEN 'Bargain'
WHEN price BETWEEN 10 and 20 THEN 'Average'
ELSE 'Gift to impress relatives'
END AS Range,
Title
FROM titles
GROUP BY
CASE
WHEN price IS NULL THEN 'Unpriced'
WHEN price < 10 THEN 'Bargain'
WHEN price BETWEEN 10 and 20 THEN 'Average'
ELSE 'Gift to impress relatives'
END,
Title
ORDER BY
CASE
WHEN price IS NULL THEN 'Unpriced'
WHEN price < 10 THEN 'Bargain'
WHEN price BETWEEN 10 and 20 THEN 'Average'
ELSE 'Gift to impress relatives'
END,
Title
GO
注意：
为了在 GROUP BY 块中使用 CASE，查询语句需要在 GROUP BY 块中重复 SELECT 块中的 CASE 块。
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