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

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

在MemSQL中执行以下操作:

-- DROP FUNCTION IF EXISTS InlineMax;
DELIMITER //
CREATE FUNCTION InlineMax(val1 INT, val2 INT) RETURNS INT AS
DECLARE
  val3 INT = 0;
BEGIN
 IF val1 > val2 THEN
   RETURN val1;
 ELSE
   RETURN val2;
 END IF; 
END //
DELIMITER ;

SELECT InlineMax(1,2) as test;

以下是一个带有NULL处理的IIF版本(基于Xin的回答):

IIF(a IS NULL OR b IS NULL, ISNULL(a,b), IIF(a > b, a, b))

逻辑如下，如果其中一个值为NULL，则返回非NULL的值(如果两个值都为NULL，则返回NULL)。否则返回较大的值。

MIN也是一样。

IIF(a IS NULL OR b IS NULL, ISNULL(a,b), IIF(a < b, a, b))

select OrderId, (
    select max([Price]) from (
        select NegotiatedPrice [Price]
        union all
        select SuggestedPrice
    ) p
) from [Order]

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