TSQL left join and only last row from right

SELECT  post.id, post.title, comment.id, comment.message 
FROM    post 
OUTER APPLY 
        ( 
        SELECT  TOP 1 * 
        FROM    comment с 
        WHERE   comment.post_id = post.id 
        ORDER BY 
                date DESC 
        ) comment 

or

SELECT  * 
FROM    ( 
        SELECT  post.id, post.title, comment.id, comment.message, 
                ROW_NUMBER() OVER (PARTITION BY post.id ORDER BY comment.date DESC) AS rn 
        FROM    post 
        LEFT JOIN 
                comment 
        ON      comment.post_id = post.id 
        ) q 
WHERE   rn = 1

The former is more efficient for few posts with many comments in each; 
the latter is more efficient for many posts with few comments in each.

from : http://stackoverflow.com/questions/2281551/tsql-left-join-and-only-last-row-from-right