Mysql GROUPing with ORDER based on auto increment column - mysql

Question

I have to group my anime index according to their AniDB ID and show the values in a DESCENDING order according to file auto increment id.
Here's what I did currently:
SELECT
f.id, f.category, f.anidb, f.mal_id, COUNT( * ) AS dupes, f.filename,
a.titles, a.synopsis, a.episodes, a.image, a.rating,
c.name as cat_name, c.id as categoryid
FROM table_files f
LEFT JOIN table_anidb a ON a.id = f.anidb
LEFT JOIN table_categories c ON c.id = f.category
GROUP BY a.id ORDER BY f.id DESC
PROBLEM:
I have Naruto 8 episodes. episode 8's ID is 204. And ep.1 has ID 160. The query return like this:
id | anidb | filename | dupes | cat_name
--------------------------------------------------------
201 | 8692 | SAO | 1 | Series
200 | 9251 | RYO | 1 | Movie
.....
.......
160 | 239 | Naruto ep.1 | 8 | Series
But I want Naruto Episode 8 to be showed in the top of the results instead of episode 1 in the last.
How do I group by anidb and mal_id at the same time with an OR logic? So that the grouping can be done even if there is not any anidb ID provided.

Answer 1

Ad. 1.
Since id, anidb and filename are all in one table i'm afraid you can't get away from doing a subquery join:
SQLFiddle
SELECT f.id, f.anidb, f.filename
FROM files f
JOIN
(SELECT MAX(id) as id FROM files GROUP BY anidb) AS f2
ON f2.id = f.id
ORDER BY f.id DESC
(data flattened for the sake of readibility but you can get the general idea)
Ad. 2.
As for the second problem, you really just have to add second grouping column to the above joined subquery:
SQLFiddle
SELECT f.id, f.anidb, f.mal_id, f.filename
FROM files f
JOIN
(SELECT MAX(id) as id FROM files GROUP BY anidb, mal_id) AS f2 on f2.id = f.id
ORDER BY f.id DESC
The NULL's are distinct from each other (e.g. NULL != NULL) so there's no fear that grouping would melt all the nulled anidb rows into one.

Answer 2

For the first problem you can use ORDER BY dupes
SELECT
f.id, f.category, f.anidb, f.mal_id, COUNT( * ) AS dupes, f.filename,
a.titles, a.synopsis, a.episodes, a.image, a.rating,
c.name as cat_name, c.id as categoryid
FROM table_files f
LEFT JOIN table_anidb a ON a.id = f.anidb
LEFT JOIN table_categories c ON c.id = f.category
GROUP BY a.id ORDER BY dupes DESC
For the second problem you can use CASE to check if f.anidb is null
SELECT
f.id, f.category, f.anidb, f.mal_id, COUNT( * ) AS dupes, f.filename,
a.titles, a.synopsis, a.episodes, a.image, a.rating,
c.name as cat_name, c.id as categoryid
FROM table_files f
LEFT JOIN table_anidb a ON a.id = f.anidb
LEFT JOIN table_categories c ON c.id = f.category
GROUP BY
(CASE WHEN f.anidb IS NULL THEN f.mal_id ELSE f.anidb END )
ORDER BY dupes DESC