SQL查询,如果value为null则返回1

Question

我有一个查询返回我们系统中设置的汇率值.并非每个订单都有汇率(currate.currentrate),因此它返回空值.

我可以让它返回1而不是null吗？

类似if语句的东西可能是:

 if isnull(currate.currentrate) then 1 else currate.currentrate 

这是我在下面的查询.我非常感谢你的帮助!

 SELECT     orderhed.ordernum, orderhed.orderdate, currrate.currencycode,  currrate.currentrate
 FROM         orderhed LEFT OUTER JOIN
                  currrate ON orderhed.company = currrate.company AND orderhed.orderdate = currrate.effectivedate

Answer 1

您可以使用CASE声明.

SELECT 
    CASE WHEN currate.currentrate IS NULL THEN 1 ELSE currate.currentrate END
FROM ...

Answer 2

你可以使用COALESCE:

SELECT  orderhed.ordernum, 
    orderhed.orderdate, 
    currrate.currencycode,  
    coalesce(currrate.currentrate, 1) as currentrate
FROM orderhed 
LEFT OUTER JOIN currrate 
    ON orderhed.company = currrate.company 
    AND orderhed.orderdate = currrate.effectivedate

甚至IsNull():

SELECT  orderhed.ordernum, 
    orderhed.orderdate, 
    currrate.currencycode,  
    IsNull(currrate.currentrate, 1) as currentrate
FROM orderhed 
LEFT OUTER JOIN currrate 
    ON orderhed.company = currrate.company 
    AND orderhed.orderdate = currrate.effectivedate

这是一篇帮助决定COALESCE和之间的文章IsNull:

http://www.mssqltips.com/sqlservertip/2689/deciding-between-coalesce-and-isnull-in-sql-server/

Answer 3

SELECT 
    ISNULL(currate.currentrate, 1)  
FROM ...

比获胜的答案更简洁,并做同样的事情

https://msdn.microsoft.com/en-us/library/ms184325.aspx

Answer 4

a) 如果你想要 0 当 value 为 null 时

SELECT isnull(PartNum,0) AS PartNumber, PartID
FROM Part

b) 如果您希望当值为 null 时为 0，否则为 1

SELECT 
  (CASE
    WHEN PartNum IS NULL THEN 0
    ELSE 1
  END) AS PartNumber,
  PartID
FROM Part