Question

I have a table with timestamped rows: say, some feed with authors:

CREATE TEMPORARY TABLE `feed` (
`id`           INT       UNSIGNED    NOT NULL    AUTO_INCREMENT    PRIMARY KEY,
`author`       VARCHAR(255)          NOT NULL,
`tm`           DATETIME              NOT NULL
);

I’d like to sort by tm DESC but in such a way that rows from one author do stick together.

For instance, having

INSERT INTO `feed` VALUES
( 5, 'peter', NOW()+1 ),
( 4, 'helen', NOW()-1 ),
( 3, 'helen', NOW()-2 ),
( 2, 'peter', NOW()-10 ),
( 1, 'peter', NOW()-11 );

The result set should be sorted by tm DESC, but all peter posts go first because his post is the most recent one. The next set of rows should originate from the author with the 2nd most recent post. And so on.

5 peter
2 peter
1 peter
3 helen
2 helen

First we sort authors by recent post, descending. Then, having this “rating”, we sort the feed with authors sorted by recent post.

Answer 1

Create in line view calculating the Min Tm and then join to it.

SELECT f.* 
FROM   feed f 
       INNER JOIN (SELECT MAX(TM) MAXTM, 
                          author 
                   FROM   Feed 
                   GROUP  BY Author)m 
         ON f.author = m.author 
ORDER  BY m.MAXTM DESC, 
          f.author 

DEMO