SQL Server 2012引入IIF:

SELECT 
    o.OrderId, 
    IIF( ISNULL( o.NegotiatedPrice, 0 ) > ISNULL( o.SuggestedPrice, 0 ),
         o.NegotiatedPrice, 
         o.SuggestedPrice 
    )
FROM 
    Order o

建议在使用IIF时处理NULL，因为boolean表达式两侧的NULL将导致IIF返回false_value(而不是NULL)。

SELECT o.OrderID
CASE WHEN o.NegotiatedPrice > o.SuggestedPrice THEN
 o.NegotiatedPrice
ELSE
 o.SuggestedPrice
END AS Price

我可能不会这样做，因为它比前面提到的CASE结构效率更低——除非您为两个查询都有覆盖索引。不管怎样，对于类似的问题，这都是一个有用的技巧:

SELECT OrderId, MAX(Price) as Price FROM (
   SELECT o.OrderId, o.NegotiatedPrice as Price FROM Order o
   UNION ALL
   SELECT o.OrderId, o.SuggestedPrice as Price FROM Order o
) as A
GROUP BY OrderId

其他答案都很好，但如果你不得不担心有NULL值，你可能会想要这个变体:

SELECT o.OrderId, 
   CASE WHEN ISNULL(o.NegotiatedPrice, o.SuggestedPrice) > ISNULL(o.SuggestedPrice, o.NegotiatedPrice)
        THEN ISNULL(o.NegotiatedPrice, o.SuggestedPrice)
        ELSE ISNULL(o.SuggestedPrice, o.NegotiatedPrice)
   END
FROM Order o

最简单的形式是……

CREATE FUNCTION fnGreatestInt (@Int1 int, @Int2 int )
RETURNS int
AS
BEGIN

    IF @Int1 >= ISNULL(@Int2,@Int1)
        RETURN @Int1
    ELSE
        RETURN @Int2

    RETURN NULL --Never Hit

END

SELECT o.OrderId,   
--MAX(o.NegotiatedPrice, o.SuggestedPrice)  
(SELECT MAX(v) FROM (VALUES (o.NegotiatedPrice), (o.SuggestedPrice)) AS value(v)) as ChoosenPrice  
FROM Order o