SQL Server 2008中没有，但GREATEST和LEAST函数现在可用于SQL Server 2022和SQL Server的云版本
对于以前的版本，您可以使用子查询可以访问外部查询中的列这一事实，这样您就可以添加一个子查询从这些查询的并集中选择max。

SELECT *, 
      (SELECT MAX(c) FROM (VALUES(number),(status)) T (c)) AS Greatest
FROM master..spt_values

或用于SQL Server 2000/2005

SELECT *, 
      (SELECT MAX(c) FROM 
                    (SELECT number AS c 
                     UNION ALL 
                     SELECT status) T) AS GreatestNumberOrStatus
FROM master..spt_values

为此，我创建了一个标量函数，如下所示：

CREATE FUNCTION [dbo].[MaxOrNull](@val1 int, @val2 int)
returns int
as
begin
    if @val1 >= @val2 RETURN @val1
    if @val1 < @val2 RETURN @val2

    RETURN NULL
end

这是最优雅的解决方案，可以在SQL代码中的任何地方使用。

我建议采用以下解决方案：

SELECT (CASE WHEN t.createdt < t.changedt THEN t.changedt ELSE t.created END) AS ChgDate
  FROM table t

可能的解决方案：

Create FUNCTION [dbo].[MaxOf]
    (
      @val1 INT =0,
      @val2 INT=0 ,
      @val3 INT =0,
      @val4 INT =0,
      @val5 INT =0,
      @val6 INT =0,
      @val7 INT =0,
      @val8 INT =0,
      @val9 INT =0,
      @val10 INT =0,
      @val11 INT =0,
      @val12 INT =0,
      @val13 INT =0,
      @val14 INT =0,
      @val15 INT =0,
      @val16 INT =0,
      @val17 INT =0,
      @val18 INT =0,
      @val19 INT =0,
      @val20 INT  =0)
      --OUTPUT 
     RETURNS INT  WITH SCHEMABINDING
AS  
   BEGIN
        DECLARE  @MAX AS INT ;
        SET @MAX=0
        IF isnull(@val1,0)> isnull(@MAX,0) SET @MAX=isnull(@val1,0) 
        IF isnull(@val2,0)> isnull(@MAX,0) SET @MAX=isnull(@val2,0) 
        IF isnull(@val3,0)> isnull(@MAX,0) SET @MAX=isnull(@val3,0) 
        IF isnull(@val4,0)> isnull(@MAX,0) SET @MAX=isnull(@val4,0) 
        IF isnull(@val5,0)> isnull(@MAX,0) SET @MAX=isnull(@val5,0) 
        IF isnull(@val6,0)> isnull(@MAX,0) SET @MAX=isnull(@val6,0) 
        IF isnull(@val7,0)> isnull(@MAX,0) SET @MAX=isnull(@val7,0) 
        IF isnull(@val8,0)> isnull(@MAX,0) SET @MAX=isnull(@val8,0) 
        IF isnull(@val9,0)> isnull(@MAX,0) SET @MAX=isnull(@val9,0) 
        IF isnull(@val10,0)> isnull(@MAX,0) SET @MAX=isnull(@val10,0) 
        IF isnull(@val11,0)> isnull(@MAX,0) SET @MAX=isnull(@val11,0) 
        IF isnull(@val12,0)> isnull(@MAX,0) SET @MAX=isnull(@val12,0) 
        IF isnull(@val13,0)> isnull(@MAX,0) SET @MAX=isnull(@val13,0) 
        IF isnull(@val14,0)> isnull(@MAX,0) SET @MAX=isnull(@val14,0) 
        IF isnull(@val15,0)> isnull(@MAX,0) SET @MAX=isnull(@val15,0) 
        IF isnull(@val16,0)> isnull(@MAX,0) SET @MAX=isnull(@val16,0) 
        IF isnull(@val17,0)> isnull(@MAX,0) SET @MAX=isnull(@val17,0) 
        IF isnull(@val18,0)> isnull(@MAX,0) SET @MAX=isnull(@val18,0) 
        IF isnull(@val19,0)> isnull(@MAX,0) SET @MAX=isnull(@val19,0) 
        IF isnull(@val20,0)> isnull(@MAX,0) SET @MAX=isnull(@val20,0) 

        RETURN @MAX ;
    END

电话号码应该是

SELECT dbo.MaxOf (2,3,4,0,0,0,0,200,8,0,0,0,0,0,0,0,0,0,0,0)

请尝试使用TOP或MAX。