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What I'm currently trying to make is an activities stream wich list :

  • The posts,
  • the comments,
  • both mixed between them and ordered by date.

My idea is to make two queries, but i don't know how to mix them up. Here are my queries :

// Query the posts :
$queryPosts = "
    SELECT * FROM $wpdb->posts
    WHERE post_type = 'post'
    AND post_status = 'publish'
    ORDER BY post_date DESC

// Query the comments :
$queryComments = "
    SELECT * FROM $wpdb->comments
    ORDER BY comment_date DESC

Is that possible with some kind of SQL JOIN ?

I tried what was suggested by @scribu about using SQL UNION and it's working well :

SELECT ID AS entry_id, post_date AS entry_date, post_content AS entry_content FROM $wpdb->posts
WHERE post_type = 'post'
AND post_status = 'publish'
SELECT comment_ID AS entry_id, comment_date AS entry_date, comment_content AS entry_content FROM $wpdb->comments
ORDER BY entry_date DESC

What I'm trying to do now is access some data which are in the posts table and not in the comments table. Any idea ?

Thanks by advance.

share|improve this question
How many of each do you want? Do you want reverse chronological? What attributes of each do you want/need? Permalink, Excerpt? More? – MikeSchinkel Mar 27 '11 at 15:53
@MikeSchinkel - "How many of each do you want?" I don't want to limit the result. "Do you want reverse chronological?" Yes. "What attributes of each do you want/need?" I just tried what was suggested by @scribu about using SQL UNION and it's working well but as you ask I have now some news problems about the data that I would like to be able to retrieve. For example I would like to access the "comment_count" which is in the posts table but doesn't have any equivalent in the comments table. – inwpitrust Mar 27 '11 at 16:38
I you have an additional question please ask another question here on the WPSE site. – MikeSchinkel Mar 28 '11 at 3:15
up vote 3 down vote accepted

I believe you're looking for SQL UNION.

share|improve this answer
Thanks for your suggestion, I updated my post. My next problem is: Each result is display in a div, I would like to be able to add a class with the type of result for each. For example: Each comment get a class="comment" and each post get a class="post". Any idea ? – inwpitrust Mar 27 '11 at 16:52
Sure, just add post_type AS entry_type and 'comment' AS entry_type columns and then check it when doing the output. – scribu Mar 27 '11 at 17:09
You can use the same trick for the comment count: comment_count and 0 AS comment_count respectively. – scribu Mar 27 '11 at 17:11
Thank you very much! – inwpitrust Mar 27 '11 at 21:33

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