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)
)

这是一个古老的答案，在很多方面都有问题。

请参阅https://stackoverflow.com/a/6871572/194653，它有更多的赞，与sql server 2008+一起工作，并处理空值等。

原创但有问题的答案:

你可以使用CASE语句:

SELECT
    CASE
        WHEN Date1 >= Date2 AND Date1 >= Date3 THEN Date1
        WHEN Date2 >= Date1 AND Date2 >= Date3 THEN Date2
        WHEN Date3 >= Date1 AND Date3 >= Date2 THEN Date3
        ELSE                                        Date1
    END AS MostRecentDate

请尝试使用UNPIVOT:

SELECT MAX(MaxDt) MaxDt
   FROM tbl 
UNPIVOT
   (MaxDt FOR E IN 
      (Date1, Date2, Date3)
)AS unpvt;

我的解决方案也可以处理空值比较。它可以被简化为一个单一的查询，但为了解释，我使用CTE。这个想法是在第一步中减少从3个数字到2个数字的比较，然后在第二步中从2个数字到1个数字的比较。

with x1 as
(
  select 1 as N1, null as N2, 3 as N3
  union
  select 1 as N1, null as N2, null as N3
  union
  select null as N1, null as N2, null as N3
)
,x2 as
(
select 
N1,N2,N3,
IIF(Isnull(N1,0)>=Isnull(N2,0),N1,N2) as max1,
IIF(Isnull(N2,0)>=Isnull(N3,0),N2,N3) as max2
from x1
)
,x3 as
(
 select N1,N2,N3,max1,max2,
 IIF(IsNull(max1,0)>=IsNull(max2,0),max1,max2) as MaxNo
 from x2
)
select * from x3

输出:

以下两个示例中的任何一个都可以工作:

SELECT  MAX(date_columns) AS max_date
FROM    ( (SELECT   date1 AS date_columns
           FROM     data_table         )
          UNION
          ( SELECT  date2 AS date_columns
            FROM    data_table
          )
          UNION
          ( SELECT  date3 AS date_columns
            FROM    data_table
          )
        ) AS date_query

第二个是对拉塞夫克的答案的补充。

SELECT  MAX(MostRecentDate)
FROM    ( SELECT    CASE WHEN date1 >= date2
                              AND date1 >= date3 THEN date1
                         WHEN date2 >= date1
                              AND date2 >= date3 THEN date2
                         WHEN date3 >= date1
                              AND date3 >= date2 THEN date3
                         ELSE date1
                    END AS MostRecentDate
          FROM      data_table
        ) AS date_query 

SELECT 
    CASE 
        WHEN Date1 >= Date2 AND Date1 >= Date3 THEN Date1 
        WHEN Date2 >= Date3 THEN Date2 
        ELSE Date3
    END AS MostRecentDate 

这样写起来稍微容易一些，因为case语句是按顺序求值的，因此跳过了求值步骤。