StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

POSingle query for selecting a random images from X unique parents?
primarykey
Id
3152160
data
AcceptedAnswerId
3169851
AnswerCount
3
ClosedDate
CommentCount
0
CommunityOwnedDate
CreationDate
2010-06-30T18:19:00.030
FavoriteCount
0
LastActivityDate
2013-03-01T12:35:03.643
LastEditDate
2013-03-01T12:35:03.643
LastEditorUserId
50776
OwnerUserId
347764
ParentId
0
PostTypeId
1
Score
0
ViewCount
521
LastEditorDisplayName
text
Body
I've used this query to randomly select a total of <code>$limit</code>-images (attachments), each from a unique and randomly selected parent. <pre><code>$query="SELECT {$wpdb->posts}.post_parent, {$wpdb->posts}.ID FROM {$wpdb->posts} INNER JOIN {$wpdb->term_relationships} ON ({$wpdb->posts}.post_parent = {$wpdb->term_relationships}.object_id) INNER JOIN {$wpdb->term_taxonomy} ON ({$wpdb->term_relationships}.term_taxonomy_id = {$wpdb->term_taxonomy}.term_taxonomy_id) WHERE {$wpdb->posts}.post_type = 'attachment' AND {$wpdb->term_taxonomy}.taxonomy = 'category' AND {$wpdb->term_taxonomy}.term_id IN ('{$wpdb->escape($category_filter)}') AND {$wpdb->posts}.post_password = '' AND {$wpdb->posts}.post_mime_type IN ('image/jpeg', 'image/gif', 'image/png') GROUP BY {$wpdb->posts}.post_parent ORDER BY {$order_by} LIMIT {$limit};"; </code></pre> (<a href="http://wordpress.org/extend/plugins/bulk-select-featured-image/" rel="nofollow noreferrer">full code at pastebin</a>) Unfortunately it has three faults: <ol> <li>I think the password-check is incorrect as it tests the attachment and not the parent_post, right? (does WordPress even support password protected gallery attachments?)</li> <li>it certainly doesn't check the parent for <code>post_status = "publish"</code></li> <li>it correctly selects random posts, but always the same pictures within them (the first one). </li> </ol> So - I humbly ask for your SQL-fu. How does one both select a random parent (first checking for published status) and then a random image ID owned by that parent, all in one query? (I could select all attachments, ordered randomly and loop through them all and just grab the first <code>$limit</code>from unique parents. But that leads to parents with lots of images getting selected too often.) <hr> "When the answer escapes you, change the question..." I just released <a href="http://wordpress.org/extend/plugins/bulk-select-featured-image/" rel="nofollow noreferrer">a plugin</a> that enables bulk selection of a “featured post image”, directly from the media library. The core of my function went from ~45 lines to this; <pre><code>foreach($potential_parents as $parent){ if(has_post_thumbnail($parent->ID)) { $image = get_post_thumbnail_id($parent->ID); } } </code></pre> It's not random but the site looks better and visitors have an easier time navigating content now that the thumbnails are consistent. 
Tags
<mysql><wordpress>
Title
Single query for selecting a random images from X unique parents?
singulars
PostAcceptedAnswerId
1. PO
 singulars
 PostTypePostTypeId
 PTAnswer
PostParentId
1. This table or related slice is empty.
PostTypePostTypeId
1. PTQuestion
UserLastEditorUserId
1. UScasperOne
UserOwnerUserId
1. USulfben
plurals
PostLinksPostIdRelatedPostId
1. This table or related slice is empty.
PostLinksRelatedPostIdPostId
1. This table or related slice is empty.
PostsAcceptedAnswerId
1. This table or related slice is empty.
PostsParentIdCreationDate
1. PO
 singulars
 PostTypePostTypeId
 PTAnswer
2. PO
 singulars
 PostTypePostTypeId
 PTAnswer
3. PO
 singulars
 PostTypePostTypeId
 PTAnswer
VotesPostIdCreationDate
1. This table or related slice is empty.
CommentsPostId
1. This table or related slice is empty.

Querying!

Guidance

A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.