sql - IF 语句附近的语法不正确

Question

我使用 IF 语句来选择 SQL SELECT 过程中不为 NULL 的列。但是，我收到一条错误消息，指出关键字 IF 附近的语法有问题。

DECLARE @imgURL_prefix VARCHAR(100)
DECLARE @imgSmall_Suffix VARCHAR(100)
DECLARE @imgLarge_Suffix VARCHAR(100)

SET @imgURL_prefix = '//sohimages.com/images/images_soh/'
SET @imgSmall_Suffix = '-1.jpg'
SET @imgLarge_Suffix = '-2.jpg'

SELECT
    P.ProductCode as ProductCode,
    P.HideProduct as HideProduct,
    P.Photos_Cloned_From as Photos_Cloned_From,
    @imgURL_prefix +
        LOWER( IF P.Photos_Cloned_From IS NOT NULL
            P.Photos_Cloned_From
        ELSE
            P.ProductCode
        END )
        + @imgSmall_Suffix as PhotoURL_Small,
    @imgURL_prefix +
        LOWER( IF P.Photos_Cloned_From IS NOT NULL
            P.Photos_Cloned_From
        ELSE
            P.ProductCode
        END )
        + @imgLarge_Suffix as PhotoURL_Large,
    P.PhotoURL_Small as OriginalSmall,
    P.PhotoURL_Large as OriginalLarge
FROM
    Products_Joined P

该脚本无需 IF 语句即可正常工作，只需在其位置使用 LOWER(P.ProductCode) 即可。

Answer 1

您可以在 sql server 2012 及更高版本中使用 IIF(Expression, true, false)，对于旧版本，您可以使用 CASE 语句

/*********  SQL SERVER 2012+ ***********/

SELECT
    P.ProductCode as ProductCode,
    P.HideProduct as HideProduct,
    P.Photos_Cloned_From as Photos_Cloned_From,
    @imgURL_prefix +
        LOWER( IIF( P.Photos_Cloned_From IS NOT NULL , P.Photos_Cloned_From, P.ProductCode))
        + @imgSmall_Suffix as PhotoURL_Small,
    @imgURL_prefix +
        LOWER( IIF (P.Photos_Cloned_From IS NOT NULL, P.Photos_Cloned_From, P.ProductCode))
        + @imgLarge_Suffix as PhotoURL_Large,
    P.PhotoURL_Small as OriginalSmall,
    P.PhotoURL_Large as OriginalLarge
FROM
    Products_Joined P

/*********  SQL SERVER Older Versions ***********/

SELECT
    P.ProductCode as ProductCode,
    P.HideProduct as HideProduct,
    P.Photos_Cloned_From as Photos_Cloned_From,
    @imgURL_prefix +
        LOWER( CASE WHEN P.Photos_Cloned_From IS NOT NULL 
              THEN P.Photos_Cloned_From ELSE P.ProductCode END)
        + @imgSmall_Suffix as PhotoURL_Small,
    @imgURL_prefix +
        LOWER( CASE WHEN P.Photos_Cloned_From IS NOT NULL 
               THEN P.Photos_Cloned_From ELSE P.ProductCode END)
        + @imgLarge_Suffix as PhotoURL_Large,
    P.PhotoURL_Small as OriginalSmall,
    P.PhotoURL_Large as OriginalLarge
FROM
    Products_Joined P