这里有一个案例示例，应该处理null，并将与旧版本的MSSQL一起工作。这是基于一个流行例子中的内联函数:

case
  when a >= b then a
  else isnull(b,a)
end

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

你可以这样做:

select case when o.NegotiatedPrice > o.SuggestedPrice 
then o.NegotiatedPrice
else o.SuggestedPrice
end

其实很简单:

CREATE FUNCTION InlineMax
(
    @p1 sql_variant,
    @p2 sql_variant
)  RETURNS sql_variant
AS
BEGIN
    RETURN CASE 
        WHEN @p1 IS NULL AND @p2 IS NOT NULL THEN @p2 
        WHEN @p2 IS NULL AND @p1 IS NOT NULL THEN @p1
        WHEN @p1 > @p2 THEN @p1
        ELSE @p2 END
END;

如果你使用的是SQL Server 2008(或更高版本)，那么这是更好的解决方案:

SELECT o.OrderId,
       (SELECT MAX(Price)
        FROM (VALUES (o.NegotiatedPrice),(o.SuggestedPrice)) AS AllPrices(Price))
FROM Order o

所有的信用和投票都应该去Sven对一个相关问题的答案，“多列的SQL MAX ?” 我说这是“最佳答案”，因为:

It doesn't require complicating your code with UNION's, PIVOT's, UNPIVOT's, UDF's, and crazy-long CASE statments. It isn't plagued with the problem of handling nulls, it handles them just fine. It's easy to swap out the "MAX" with "MIN", "AVG", or "SUM". You can use any aggregate function to find the aggregate over many different columns. You're not limited to the names I used (i.e. "AllPrices" and "Price"). You can pick your own names to make it easier to read and understand for the next guy. You can find multiple aggregates using SQL Server 2008's derived_tables like so: SELECT MAX(a), MAX(b) FROM (VALUES (1, 2), (3, 4), (5, 6), (7, 8), (9, 10) ) AS MyTable(a, b)

我会使用kcrumley提供的解决方案 只需稍微修改它以处理null

create function dbo.HigherArgumentOrNull(@val1 int, @val2 int)
returns int
as
begin
  if @val1 >= @val2
    return @val1
  if @val1 < @val2
    return @val2

 return NULL
end

编辑 在Mark的评论后修改。正如他在3值逻辑x > NULL或x < NULL应该总是返回NULL。换句话说，未知的结果。