I did multiple searches for an answer to this (on SO and elsewhere), but haven't found an answer that really fit my needs (if it's out there, I apologize in advance).
I have a query, using PHP, that returns an array from a database (WordPress). Basically what I want to do is look at a column's value, and then LIMIT based on that value. Here's the array that's returned for a better idea:
In the query, you'll notice that the value for post_parent repeats for several of returned arrays. What I want to do is have it LIMIT to 3 based on the post_parent value e.g. I want 3 entries for post_parent 79, 87, 100, etc.
I'm not well versed (see: at all) in MySQL queries, but this is what I have to get that array:
SELECT DISTINCT ID, guid, post_parent, post_title
FROM $wpdb->posts p
WHERE p.post_type = 'attachment'
AND p.post_mime_type LIKE 'image/%'
AND p.post_status = 'inherit'
AND p.post_parent IN
(SELECT object_id FROM $term_relationships WHERE term_taxonomy_id = $post_term)
I've tried using GROUP BY, but that didn't get me what I wanted. Any help is appreciated.
EDIT Just to clarify, these are the results I want: http://pastebin.com/pWXdUuXv
This might do the trick: (I'm assuming ID is unique, if not substitute something that is)
SELECT
p.ID, guid, post_parent, post_title
FROM (
SELECT
a.ID as ID,
COUNT(*) as rank
FROM (
SELECT ID, post_parent
FROM $wpdb->posts
WHERE post_type = 'attachment'
AND post_mime_type LIKE 'image/%'
AND post_status = 'inherit'
) AS a
JOIN (
SELECT ID, post_parent
FROM $wpdb->posts
WHERE post_type = 'attachment'
AND post_mime_type LIKE 'image/%'
AND post_status = 'inherit'
) AS b ON b.ID <= a.ID AND b.post_parent = a.post_parent
GROUP BY a.ID
) AS r
JOIN $wpdb->posts p ON r.ID = p.ID AND r.rank <= 3
WHERE p.post_parent IN (
SELECT object_id FROM $term_relationships
WHERE term_taxonomy_id = $post_term)
GROUP BY p.ID
;
EDIT: Attempt to include category in rank so it'll actually work.
Specifying conditions twice is a bit ugly, but I didn't see an easy way around it.