SQL Server 2017

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CREATE TABLE DxList (
DocID int,
Dx varchar(255),
DxDate date,
CreateDate datetime);
INSERT INTO DxList (DocID, Dx, DxDate, CreateDate)
VALUES (6014, 'OSDD',  '10/01/2015',  '10/09/2015 12:27');
INSERT INTO DxList (DocID, Dx, DxDate, CreateDate)
VALUES (6018, 'ADHD', '10/01/2015', '10/09/2015 18:14' );
2 rows affected

SELECT DocID, Dx, DxDate, CreateDate
FROM
(
    SELECT *,
        ROW_NUMBER() OVER (PARTITION BY DocID ORDER BY DxDate DESC, CreateDate DESC) rn
    FROM DxList
) t
WHERE rn = 1;


DocID
Dx
DxDate
CreateDate


6014
OSDD
01/10/2015 00:00:00
09/10/2015 12:27:00

6018
ADHD
01/10/2015 00:00:00
09/10/2015 18:14:00


SELECT top 1 *
       
    FROM DxList
    order by DxDate desc,CreateDate desc


DocID
Dx
DxDate
CreateDate


6018
ADHD
01/10/2015 00:00:00
09/10/2015 18:14:00

DocID	Dx	DxDate	CreateDate
6014	OSDD	01/10/2015 00:00:00	09/10/2015 12:27:00
6018	ADHD	01/10/2015 00:00:00	09/10/2015 18:14:00