如果您正在使用SQL Server 2005，您可以使用UNPIVOT特性。下面是一个完整的例子:

create table dates 
(
  number int,
  date1 datetime,
  date2 datetime,
  date3 datetime 
)

insert into dates values (1, '1/1/2008', '2/4/2008', '3/1/2008')
insert into dates values (1, '1/2/2008', '2/3/2008', '3/3/2008')
insert into dates values (1, '1/3/2008', '2/2/2008', '3/2/2008')
insert into dates values (1, '1/4/2008', '2/1/2008', '3/4/2008')

select max(dateMaxes)
from (
  select 
    (select max(date1) from dates) date1max, 
    (select max(date2) from dates) date2max,
    (select max(date3) from dates) date3max
) myTable
unpivot (dateMaxes For fieldName In (date1max, date2max, date3max)) as tblPivot

drop table dates

您可以创建一个函数，其中传递日期，然后将该函数添加到select语句，如下所示。 select Number, dbo.fxMost_Recent_Date(Date1,Date2,Date3)，成本

create FUNCTION  fxMost_Recent_Date 

（ @Date1 smalldatetime, @Date2 smalldatetime, @Date3 smalldatetime ） 返回smalldatetime 作为 开始 DECLARE @Result smalldatetime

declare @MostRecent smalldatetime

set @MostRecent='1/1/1900'

if @Date1>@MostRecent begin set @MostRecent=@Date1 end
if @Date2>@MostRecent begin set @MostRecent=@Date2 end
if @Date3>@MostRecent begin set @MostRecent=@Date3 end
RETURN @MostRecent

END

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)
)

我更喜欢基于case-when的解决方案，我的假设是，与其他可能的解决方案(如交叉应用、values()、自定义函数等)相比，它对可能的性能下降的影响应该最小。

下面是case-when版本，它在大多数可能的测试用例中处理空值:

SELECT
    CASE 
        WHEN Date1 > coalesce(Date2,'0001-01-01') AND Date1 > coalesce(Date3,'0001-01-01') THEN Date1 
        WHEN Date2 > coalesce(Date3,'0001-01-01') THEN Date2 
        ELSE Date3
    END AS MostRecentDate
    , *
from 
(values
     (  1, cast('2001-01-01' as Date), cast('2002-01-01' as Date), cast('2003-01-01' as Date))
    ,(  2, cast('2001-01-01' as Date), cast('2003-01-01' as Date), cast('2002-01-01' as Date))
    ,(  3, cast('2002-01-01' as Date), cast('2001-01-01' as Date), cast('2003-01-01' as Date))
    ,(  4, cast('2002-01-01' as Date), cast('2003-01-01' as Date), cast('2001-01-01' as Date))
    ,(  5, cast('2003-01-01' as Date), cast('2001-01-01' as Date), cast('2002-01-01' as Date))
    ,(  6, cast('2003-01-01' as Date), cast('2002-01-01' as Date), cast('2001-01-01' as Date))
    ,( 11, cast(NULL         as Date), cast('2002-01-01' as Date), cast('2003-01-01' as Date))
    ,( 12, cast(NULL         as Date), cast('2003-01-01' as Date), cast('2002-01-01' as Date))
    ,( 13, cast('2003-01-01' as Date), cast(NULL         as Date), cast('2002-01-01' as Date))
    ,( 14, cast('2002-01-01' as Date), cast(NULL         as Date), cast('2003-01-01' as Date))
    ,( 15, cast('2003-01-01' as Date), cast('2002-01-01' as Date), cast(NULL         as Date))
    ,( 16, cast('2002-01-01' as Date), cast('2003-01-01' as Date), cast(NULL         as Date))
    ,( 21, cast('2003-01-01' as Date), cast(NULL         as Date), cast(NULL         as Date))
    ,( 22, cast(NULL         as Date), cast('2003-01-01' as Date), cast(NULL         as Date))
    ,( 23, cast(NULL         as Date), cast(NULL         as Date), cast('2003-01-01' as Date))
    ,( 31, cast(NULL         as Date), cast(NULL         as Date), cast(NULL         as Date))

) as demoValues(id, Date1,Date2,Date3)
order by id
;

结果是:

MostRecent    id   Date1      Date2      Date3
2003-01-01    1    2001-01-01 2002-01-01 2003-01-01
2003-01-01    2    2001-01-01 2003-01-01 2002-01-01
2003-01-01    3    2002-01-01 2001-01-01 2002-01-01
2003-01-01    4    2002-01-01 2003-01-01 2001-01-01
2003-01-01    5    2003-01-01 2001-01-01 2002-01-01
2003-01-01    6    2003-01-01 2002-01-01 2001-01-01
2003-01-01    11   NULL       2002-01-01 2003-01-01
2003-01-01    12   NULL       2003-01-01 2002-01-01
2003-01-01    13   2003-01-01 NULL       2002-01-01
2003-01-01    14   2002-01-01 NULL       2003-01-01
2003-01-01    15   2003-01-01 2002-01-01 NULL
2003-01-01    16   2002-01-01 2003-01-01 NULL
2003-01-01    21   2003-01-01 NULL       NULL
2003-01-01    22   NULL       2003-01-01 NULL
2003-01-01    23   NULL       NULL       2003-01-01
NULL          31   NULL       NULL       NULL

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。

从SQL Server 2012我们可以使用IIF。

 DECLARE @Date1 DATE='2014-07-03';
 DECLARE @Date2 DATE='2014-07-04';
 DECLARE @Date3 DATE='2014-07-05';

 SELECT IIF(@Date1>@Date2,
        IIF(@Date1>@Date3,@Date1,@Date3),
        IIF(@Date2>@Date3,@Date2,@Date3)) AS MostRecentDate