 
select getdate() as 日期,case month(getdate()) 
when 11 then '十一' 
when 12 then '十二' 
else substring('一二三四五六七八九十', month(getdate()),1) 
end+'月' as 月份 

CASE 可能是 SQL 中被誤用最多的關(guān)鍵字之一。雖然你可能以前用過這個關(guān)鍵字來創(chuàng)建字段，但是它還具有更多用法。例如，你可以在 WHERE 子句中使用 CASE。

首先讓我們看一下 CASE 的語法。在一般的 SELECT 中，其語法如下：

復(fù)制代碼代碼如下:

 
SELECT <myColumnSpec> = 
CASE 
WHEN <A> THEN <somethingA> 
WHEN <B> THEN <somethingB> 
ELSE <somethingE> 
END 

在上面的代碼中需要用具體的參數(shù)代替尖括號中的內(nèi)容。下面是一個簡單的例子：

復(fù)制代碼代碼如下:

 
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 

這是 CASE 的典型用法，但是使用 CASE 其實可以做更多的事情。比方說下面的 GROUP BY 子句中的 CASE：

復(fù)制代碼代碼如下:

 
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 

你甚至還可以組合這些選項，添加一個 ORDER BY 子句，如下所示：

復(fù)制代碼代碼如下:

 
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 