Scalar Function cause all sorts of performance issues, so its better to wrap the logic into an Inline Table Valued Function if possible. This is the function I used to replace some User Defined Functions which selected the Min/Max dates from a list of upto ten dates. When tested on my dataset of 1 Million rows the Scalar Function took over 15 minutes before I killed the query the Inline TVF took 1 minute which is the same amount of time as selecting the resultset into a temporary table. To use this call the function from either a subquery in the the SELECT or a CROSS APPLY.

CREATE FUNCTION dbo.Get_Min_Max_Date
(
    @Date1  datetime,
    @Date2  datetime,
    @Date3  datetime,
    @Date4  datetime,
    @Date5  datetime,
    @Date6  datetime,
    @Date7  datetime,
    @Date8  datetime,
    @Date9  datetime,
    @Date10 datetime
)
RETURNS TABLE
AS
RETURN
(
    SELECT      Max(DateValue)  Max_Date,
                Min(DateValue)  Min_Date
    FROM        (
                    VALUES  (@Date1),
                            (@Date2),
                            (@Date3),
                            (@Date4),
                            (@Date5),
                            (@Date6),
                            (@Date7),
                            (@Date8),
                            (@Date9),
                            (@Date10)
                )   AS Dates(DateValue)
)

另一种使用CASE WHEN的方法

SELECT CASE true 
       WHEN max(row1) >= max(row2) THEN CASE true WHEN max(row1) >= max(row3) THEN max(row1) ELSE max(row3) end ELSE
       CASE true WHEN max(row2) >= max(row3) THEN max(row2) ELSE max(row3) END END
FROM yourTable

下面是使用T-SQL和SQL Server实现Max功能的另一个很好的解决方案

SELECT [Other Fields],
  (SELECT Max(v) 
   FROM (VALUES (date1), (date2), (date3),...) AS value(v)) as [MaxDate]
FROM [YourTableName]

Values是表值构造函数。

"指定要构造到表中的一组行值表达式。Transact-SQL表值构造函数允许在单个DML语句中指定多行数据。表值构造函数可以指定为INSERT…VALUES语句，或者作为MERGE语句的USING子句或FROM子句中的派生表。

上表为员工工资表，列为salary1、salary2、salary3、salary4。下面的查询将返回四列中的最大值

select  
 (select Max(salval) from( values (max(salary1)),(max(salary2)),(max(salary3)),(max(Salary4)))alias(salval)) as largest_val
 from EmployeeSalary

运行上述查询将输出largest_val(10001)

上述查询逻辑如下:

select Max(salvalue) from(values (10001),(5098),(6070),(7500))alias(salvalue)

输出将是10001

For T-SQL (MSSQL 2008+)

SELECT
  (SELECT
     MAX(MyMaxName) 
   FROM ( VALUES 
            (MAX(Field1)), 
            (MAX(Field2)) 
        ) MyAlias(MyMaxName)
  ) 
FROM MyTable1

DECLARE @TableName TABLE (Number INT, Date1 DATETIME, Date2 DATETIME, Date3 DATETIME, Cost MONEY)

INSERT INTO @TableName 
SELECT 1, '20000101', '20010101','20020101',100 UNION ALL
SELECT 2, '20000101', '19900101','19980101',99 

SELECT Number,
       Cost  ,
       (SELECT MAX([Date])
       FROM    (SELECT Date1 AS [Date]
               UNION ALL
               SELECT Date2
               UNION ALL
               SELECT Date3
               )
               D
       )
       [Most Recent Date]
FROM   @TableName