Retrieving only the last row of a table, in the absence of a primary key
If you want the row with the highest offset value for each file, then:

;WITH x AS (SELECT [Column 1], [Column 2], [Column 3],
  rn = ROW_NUMBER() OVER (PARTITION BY [Column 2] ORDER BY [Column 3] DESC
  FROM dbo.source_table
)
SELECT [Column 1], [Column 2], [Column 3]
  FROM x
  WHERE rn = 1
  ORDER BY [Column 2];


If yu just want the row with the highest offset across all files, you don't want MAX(), but you can use TOP (1):

SELECT TOP (1) [Column 1], [Column 2], [Column 3]
  FROM dbo.source_table
  ORDER BY [Column 3] DESC;