当value为null时,在查询中设置默认值

Question

我正在运行一个非常简单的查询,但是对于某些结果,一个字段中的值为null.如果值为null,如何将该值设置为"字符串"？

就像是

SELECT RegName,
    RegEmail,
    RegPhone,
    RegOrg,
    RegCountry,
    DateReg,
    (Website IS NULL? 'no website' : Website) AS WebSite
FROM RegTakePart
WHERE Reject IS NULL

它将在sql server 2005上运行

谢谢

Answer 1

使用以下内容:

SELECT RegName,
       RegEmail,
       RegPhone,
       RegOrg,
       RegCountry,
       DateReg,
       ISNULL(Website,'no website')  AS WebSite 
FROM   RegTakePart 
WHERE  Reject IS NULL

或者,@ Lieven指出:

SELECT RegName,
       RegEmail,
       RegPhone,
       RegOrg,
       RegCountry,
       DateReg,
       COALESCE(Website,'no website')  AS WebSite 
FROM   RegTakePart 
WHERE  Reject IS NULL

COALESCE的动态是你可以定义更多的参数,所以如果第一个是null然后得到第二个,如果第二个是null得到第三个等等...

Answer 2

如上所述，聚结溶液是优选的。作为一个额外的好处，您可以对“派生”值与选定值使用合并，如下所示：

SELECT
       {stuff},
       COALESCE( (select count(*) from tbl where {stuff} ), 0 )  AS countofstuff
FROM
       tbl
WHERE
       {something}

使用“iif”或“case”，您需要重复内联，而使用coalesce则不需要，它允许您避免在该返回中出现“null”结果......

Answer 3

用途CASE:

SELECT regname, 
       regemail, 
       regphone, 
       regorg, 
       regcountry, 
       datereg, 
       CASE 
         WHEN website IS NULL THEN 'no website' 
         ELSE website 
       END AS WebSite 
FROM   regtakepart 
WHERE  reject IS NULL 

或者COALESCE:

....
COALESCE(website, 'no website') AS WebSite 
....