SELECT  
(CASE 
     WHEN (Obsolete = 'N' OR InStock = 'Y') THEN 'YES'
                                            ELSE 'NO' 
 END) as Salable
, * 
FROM Product

作为CASE语句的替代解决方案，可以使用表驱动方法：

DECLARE @Product TABLE (ID INT, Obsolete VARCHAR(10), InStock VARCHAR(10))
INSERT INTO @Product VALUES
(1,'N','Y'),
(2,'A','B'),
(3,'N','B'),
(4,'A','Y')

SELECT P.* , ISNULL(Stmt.Saleable,0) Saleable
FROM
    @Product P
    LEFT JOIN
        ( VALUES
            ( 'N', 'Y', 1 )
        ) Stmt (Obsolete, InStock, Saleable)
        ON  P.InStock = Stmt.InStock OR P.Obsolete = Stmt.Obsolete

结果：

ID          Obsolete   InStock    Saleable
----------- ---------- ---------- -----------
1           N          Y          1
2           A          B          0
3           N          B          1
4           A          Y          1

SQL Server中的简单if-else语句：

DECLARE @val INT;
SET @val = 15;

IF @val < 25
PRINT 'Hi Ravi Anand';
ELSE
PRINT 'By Ravi Anand.';

GO

SQL Server中嵌套的If…else语句-

DECLARE @val INT;
SET @val = 15;

IF @val < 25
PRINT 'Hi Ravi Anand.';
ELSE
BEGIN
IF @val < 50
  PRINT 'what''s up?';
ELSE
  PRINT 'Bye Ravi Anand.';
END;

GO

你可以在SQL CASE语句的威力中找到一些很好的例子，我认为你可以使用的语句应该是这样的（来自4guysfromrolla）：

SELECT
    FirstName, LastName,
    Salary, DOB,
    CASE Gender
        WHEN 'M' THEN 'Male'
        WHEN 'F' THEN 'Female'
    END
FROM Employees

SELECT 1 AS Saleable, *
  FROM @Product
 WHERE ( Obsolete = 'N' OR InStock = 'Y' )
UNION
SELECT 0 AS Saleable, *
  FROM @Product
 WHERE NOT ( Obsolete = 'N' OR InStock = 'Y' )

会是这样的：

SELECT OrderID, Quantity,
CASE
    WHEN Quantity > 30 THEN "The quantity is greater than 30"
    WHEN Quantity = 30 THEN "The quantity is 30"
    ELSE "The quantity is under 30"
END AS QuantityText
FROM OrderDetails;