MySQL Order before Group by

Question

I need to find the latest post for each author and then group the results so I only a single latest post for each author.

SELECT wp_posts.* FROM wp_posts
            


        

Answer 1

When our table became large, performance need to checked also. I checked all the options in the questions here, with a PM system with a 136K messages and link table with 83K rows.

When you need only count, or only IDs - Alex's solution is the best.

SELECT wp_posts.post_author, MAX(wp_posts.post_date), wp_posts.status, wp_posts.post_type
FROM wp_posts
    WHERE wp_posts.post_status='publish'
    AND wp_posts.post_type='post'
    GROUP BY wp_posts.post_author

When you need other fields, I need to modify Husky110 solution (to my table design - here it is only example - not checked), that in my tables 10x faster than the subquery option:

SELECT wp_posts.* FROM wp_posts,
    (Select post_id as pid,  max(post_date) maxdate from wp_posts where author = ... group by author order by maxdate  desc limit 4) t
    WHERE wp_posts.post_status='publish'
    AND wp_posts.post_type='post'
    AND wp_posts.post_id = pid

This change can select more than one post (one for user, for example), and can be modified to other solutions.

Moshe.