如何在SQL SELECT语句中执行IF…THEN?

例如:

SELECT IF(Obsolete = 'N' OR InStock = 'Y' ? 1 : 0) AS Saleable, * FROM Product

当前回答

Microsoft SQL Server(T-SQL)

在选择中,使用:

select case when Obsolete = 'N' or InStock = 'Y' then 'YES' else 'NO' end

在where子句中,使用:

where 1 = case when Obsolete = 'N' or InStock = 'Y' then 1 else 0 end

其他回答

SQL Server 2012中添加了一个新功能IIF(我们可以简单使用):

SELECT IIF ( (Obsolete = 'N' OR InStock = 'Y'), 1, 0) AS Saleable, * FROM Product
 SELECT
   CASE 
      WHEN OBSOLETE = 'N' or InStock = 'Y' THEN 'TRUE' 
      ELSE 'FALSE' 
   END AS Salable,
   * 
FROM PRODUCT
SELECT CASE WHEN profile.nrefillno = 0 THEN 'N' ELSE 'R'END as newref
From profile

Microsoft SQL Server(T-SQL)

在选择中,使用:

select case when Obsolete = 'N' or InStock = 'Y' then 'YES' else 'NO' end

在where子句中,使用:

where 1 = case when Obsolete = 'N' or InStock = 'Y' then 1 else 0 end

使用纯位逻辑:

DECLARE @Product TABLE (
    id INT PRIMARY KEY IDENTITY NOT NULL
   ,Obsolote CHAR(1)
   ,Instock CHAR(1)
)

INSERT INTO @Product ([Obsolote], [Instock])
    VALUES ('N', 'N'), ('N', 'Y'), ('Y', 'Y'), ('Y', 'N')

;
WITH cte
AS
(
    SELECT
        'CheckIfInstock' = CAST(ISNULL(NULLIF(ISNULL(NULLIF(p.[Instock], 'Y'), 1), 'N'), 0) AS BIT)
       ,'CheckIfObsolote' = CAST(ISNULL(NULLIF(ISNULL(NULLIF(p.[Obsolote], 'N'), 0), 'Y'), 1) AS BIT)
       ,*
    FROM
        @Product AS p
)
SELECT
    'Salable' = c.[CheckIfInstock] & ~c.[CheckIfObsolote]
   ,*
FROM
    [cte] c

请参阅SQL Server中的工作演示:if then without case。

首先,需要计算所选条件的true和false值。下面是两个NULLIF:

for true: ISNULL(NULLIF(p.[Instock], 'Y'), 1)
for false: ISNULL(NULLIF(p.[Instock], 'N'), 0)

组合在一起得到1或0。接下来使用按位运算符。

这是最WYSIWYG的方法。