Selecting most recent date between two columns

问题:

If I have a table that (among other columns) has two DATETIME columns, how would I select the most recent date from those two columns.

Example:

ID     Date1     Date2

1      1/1/2008   2/1/2008

2      2/1/2008   1/1/2008

3      1/10/2008  1/10/2008

If I wanted my results to look like

ID     MostRecentDate

1      2/1/2008

2      2/1/2008

3      1/10/2008

Is there a simple way of doing this that I am obviously overlooking? I know I can do subqueries and case statements or even write a function in sql server to handle it, but I had it in my head that there was a max-compare type function already built in that I am just forgetting about.

回答1:

CASE is IMHO your best option:

SELECT ID,
       CASE WHEN Date1 > Date2 THEN Date1
            ELSE Date2
       END AS MostRecentDate
FROM Table

---

If one of the columns is nullable just need to enclose in COALESCE:

.. COALESCE(Date1, '1/1/1973') > COALESCE(Date2, '1/1/1973')

回答2:

select ID, 
case
when Date1 > Date2 then Date1
else Date2
end as MostRecentDate
from MyTable

回答3:

You can throw this into a scalar function, which makes handling nulls a little easier. Obviously it isn't going to be any faster than the inline case statement.

ALTER FUNCTION [fnGetMaxDateTime] (
    @dtDate1        DATETIME,
    @dtDate2        DATETIME
) RETURNS DATETIME AS
BEGIN
    DECLARE @dtReturn DATETIME;

    -- If either are NULL, then return NULL as cannot be determined.
    IF (@dtDate1 IS NULL) OR (@dtDate2 IS NULL)
        SET @dtReturn = NULL;

    IF (@dtDate1 > @dtDate2)
        SET @dtReturn = @dtDate1;
    ELSE
        SET @dtReturn = @dtDate2;

    RETURN @dtReturn;
END

回答4:

I think the accepted answer is the simplest. However, I would watch for null values in the dates...

SELECT ID,
       CASE WHEN ISNULL(Date1,'01-01-1753') > ISNULL(Date2,'01-01-1753') THEN Date1
            ELSE Date2
       END AS MostRecentDate
FROM Table

回答5:

From SQL Server 2012 it's possible to use the shortcut IIF to CASE expression though the latter is SQL Standard:

SELECT ID,
       IIF(DateColA > DateColB, DateColA, DateColB) AS MostRecentDate
  FROM theTable

回答6:

Whenever possible, use InLine functions as they suffer none of the performance issues generally associated with UDFs...

Create FUNCTION MaximumDate 
(   
@DateTime1 DateTime,
@DateTime2 DateTime
)
RETURNS TABLE 
AS
RETURN 
(
    Select Case When @DateTime1 > @DateTime2 Then @DateTime1
                Else @DateTime2 End MaxDate
)
GO 

For usage guidelines, see Here

回答7:

Other than case statement, I don't believe so...

  Select Case When DateColA > DateColB Then DateColA 
              Else DateColB End MostRecent
  From Table ... 

回答8:

AFAIK, there is no built-in function to get the maximum of two values, but you can write your own easily as:

CREATE FUNCTION dbo.GetMaximumDate(@date1 DATETIME, @date2 DATETIME)
RETURNS DATETIME
AS
BEGIN
    IF (@date1 > @date2)
        RETURN @date1
    RETURN @date2
END

and call it as

SELECT Id, dbo.GetMaximumDate(Date1, Date2)
FROM tableName

回答9:

This thread has several solutions. If you had more than 2 dates to compare, "unpivot" might be preferable to writing a series of case statements. The following is blatantly stolen from Niikola:

select id, max(dDate) MostRecentDate
  from YourTable
    unpivot (dDate for nDate in (Date1, Date2, Date3)) as u
  group by id 

Then you can order by dDate, if that's helpful.

回答10:

All other correct answers as already posted.

But if you are still really looking for MAX keyword then here is a way :

select ID , MAX(dt) from 
(  select Id , Date1 as dt from table1
   union  
   select ID , Date2 from table2
) d
group by d.Id

回答11:

select max(d) ChangeDate
from (values(@d), (@d2)) as t(d)

回答12:

select ID,(select max(d) from (select Date1 d uninon select Date2 d) as t) as MaxDate
from MyTable

回答13:

Why couldn't you use the GREATEST function?

select id, date1, date2, GREATEST( nvl(date1,date2) , nvl(date2, date1) )
from table1;

I included a NVL to ensure that NULL was evaluated correctly, otherwise if either Date1 or Date2 is null, the Greatest returns NULL.

ID  Date1       Date2       MostRecentDate
1   1/1/2008    2/1/2008    2/1/2008
2   2/1/2008    1/1/2008    2/1/2008
3   1/10/2008   1/10/2008   1/10/2008
4   -null-      2/10/2008   2/10/2008
5   2/10/2008   -null-      2/10/2008