A   B	C	2009-05-04 19:30:52.847
A   B	D	2009-05-04 19:30:55.050
A   B	E	2009-05-04 19:30:57.003

CREATE TABLE TestTable (
  ColumnA     NVARCHAR(10),
  ColumnB     NVARCHAR(10),
  ColumnC     NVARCHAR(10),
  CreatedDate DATETIME    DEFAULT Getutcdate())

INSERT INTO TestTable(ColumnA, ColumnB, ColumnC) VALUES ('A', 'B', 'C');
INSERT INTO TestTable(ColumnA, ColumnB, ColumnC) VALUES ('A', 'B', 'D');
INSERT INTO TestTable(ColumnA, ColumnB, ColumnC) VALUES ('A', 'B', 'E');

SELECT *
FROM   TestTable
WHERE  CreatedDate = (SELECT   Max(CreatedDate)
                      FROM     TestTable
                      WHERE    ColumnA = 'A'
                               AND ColumnB = 'B'
                      GROUP BY ColumnA,
                               ColumnB)

SELECT top 1 *
FROM   TestTable
order by CreatedDate desc

SELECT
     T1.column_a,
     T1.column_b,
     T1.column_c,
     T1.created_date
FROM
     dbo.Test_Table T1
WHERE
     T1.column_a = 'A' AND
     T1.column_b = 'B' AND
     NOT EXISTS
     (
          SELECT
               *
          FROM
               dbo.Test_Table T2
          WHERE
               T2.column_a = T1.column_a AND
               T2.column_b = T1.column_b AND
               T2.created_date > T1.created_date
     )

SELECT
     T1.column_a,
     T1.column_b,
     T1.column_c,
     T1.created_date
FROM
     dbo.Test_Table T1
LEFT OUTER JOIN dbo.Test_Table T2 ON
     T2.column_a = T1.column_a AND
     T2.column_b = T1.column_b AND
     T2.created_date > T1.created_date
WHERE
     T1.column_a = 'A' AND
     T1.column_b = 'B' AND
     T2.column_a IS NULL

SELECT
    T1.column_a,
    T1.column_b,
    T1.column_c,
    T1.created_date
FROM
    dbo.Test_Table T1
    JOIN (SELECT column_a,
                 column_b,
                 max(created_date) MaxDate
          FROM
                 dbo.Test_Table
          GROUP BY column_a,
                   column_b) T2
    ON  T1.column_a     = T2.column_a
    AND T1.column_b     = T2.column_b
    AND T1.created_date = T2.Maxdate

SELECT TOP 1 WITH TIES *
FROM TestTable
WHERE ColumnA = 'A'
  AND ColumnB = 'B'
ORDER BY CreatedDate DESC