sql-server,SQL Query中的IF语句

Question

我在使用IF此sql-server查询中的语句时遇到问题.

我想要的是:

如果salesHeader.[Ship-to Name]不为null,我需要返回AS DeliveryName,如果它为null,则返回其他内容.

有没有办法if在查询中使用语句执行此操作？

SELECT
   poHeader.No_ AS PONumber, 
   poHeader.[Buy-from Vendor No_] AS VendorNumber, 
   poHeader.[Document Date] AS DocDate, 
   salesHeader.GiftMessage, 
   salesHeader.[Delivery Comment] AS DeliveryComment,                     
   salesHeader.[Shipment Date] AS DeliveryDate, 
   IF salesHeader.[Ship-to Name] IS NOT NULL 
      salesHeader.[Ship-to Name] AS DeliveryName
   ELSE
      poHeader.[Ship-to Name] AS DeliveryName
   END 
FROM         
    dbo.[Crocus Live$Purch_ orders for e-mailing] AS poForEmailing 
LEFT OUTER JOIN
    dbo.[Crocus Live$Purchase Header] AS poHeader ON poForEmailing.No_ = poHeader.No_ 
INNER JOIN
    dbo.[Crocus Live$Vendor] AS vendor ON poHeader.[Buy-from Vendor No_] = vendor.No_ 
LEFT OUTER JOIN
    dbo.[Crocus Live$Sales Header] AS salesHeader ON salesHeader.No_ = dbo.fnGetSalesOrderNumber(poHeader.No_)

Answer 1

使用CASE,而不是IF

CASE 
    WHEN salesHeader.[Ship-to Name] IS NOT NULL THEN salesHeader.[Ship-to Name]
    ELSE poHeader.[Ship-to Name]
END AS DeliveryName

编辑:

对于这个特殊情况,COALESCE和ISNULL答案给出的其他答案同样有效(并且更简单,坦率地说)

Answer 2

或者使用COALESCE ......

SELECT 
COALESCE(salesHeader.[Ship-to Name], poHeader.[Ship-to Name]) AS DeliveryName

COALESCE将返回列表中的第一个非NULL值

Answer 3

你可以使用CASE:

(CASE WHEN cond-1 THEN value-if-1
      WHEN cond-2 THEN value-if-2
      ELSE default-value END) AS column-name

或者在这种情况下你可以使用COALESCE或ISNULL:

COALESCE(salesHeader.[Ship-to Name], poHeader.[Ship-to Name]) AS DeliveryName

ISNULL(salesHeader.[Ship-to Name], poHeader.[Ship-to Name]) AS DeliveryName