Return wpdb with multiple meta keys and sort by a meta_value

Question

I am trying to use the wordpress wpdb class to return custom posts with one of two values for meta keys and then sort those posts by a third meta value. I can get the posts that I want but I just can't seem to figure out how to sort them the way I would like.

The function I have so far is:

function artists_search_country($country_alt){
    global $wpdb;
    $querystr = "
        SELECT wposts.*
        FROM $wpdb->posts wposts, $wpdb->postmeta wpostmeta
        WHERE wposts.ID = wpostmeta.post_id
        AND ((wpostmeta.meta_key = '_artist_country' AND wpostmeta.meta_value = '$country_alt')
        OR (wpostmeta.meta_key = '_artist_country_sub' AND wpostmeta.meta_value = '$country_alt'))
        AND wposts.post_type = 'artists'
        AND wposts.post_status = 'publish'
    ";
    $myposts = $wpdb->get_results($querystr, OBJECT);
    return $myposts;
}

I would like to do something like:

function artists_search_country($country_alt){
    global $wpdb;
    $querystr = "
        SELECT wposts.*
        FROM $wpdb->posts wposts, $wpdb->postmeta wpostmeta
        WHERE wposts.ID = wpostmeta.post_id
        AND ((wpostmeta.meta_key = '_artist_country' AND wpostmeta.meta_value = '$country_alt')
        OR (wpostmeta.meta_key = '_artist_country_sub' AND wpostmeta.meta_value = '$country_alt'))
        AND wposts.post_type = 'artists'
        AND wposts.post_status = 'publish'
        ORDER BY (wpostmeta.meta_key = '_artist_artist_last_name' AND wpostmeta.value) ASC
    ";
    $myposts = $wpdb->get_results($querystr, OBJECT);
    return $myposts;
}

Please excuse the poor syntax on the ORDER BY line but I just don't know how to approach this one, everything I try breaks the query. Any help would be greatly appreciated as I don't have that much experience with SQL queries.

Answer 1

Try this SQL statement:

SELECT wposts.*, l.meta_value as artist_last_name
FROM $wpdb->posts wposts
    join $wpdb->postmeta wpostmeta
    on wposts.ID = wpostmeta.post_id
    join $wpdn->postmeta l
    on wposts.ID = l.post_id
    and l.meta_key = '_artist_artist_last_name'
WHERE
(( wpostmeta.meta_key = '_artist_country' AND wpostmeta.meta_value = '$country_alt')
OR (wpostmeta.meta_key = '_artist_country_sub' AND wpostmeta.meta_value = '$country_alt') )
AND wposts.post_type = 'artists'
AND wposts.post_status = 'publish'
ORDER BY l.meta_value ASC

You need to make a second join for the artist's last name.

Another recommendation is to leverage Wordpress' $wpdb->prepare , like this:

$querystr = "
SELECT wposts.*, l.meta_value as artist_last_name
FROM $wpdb->posts wposts
    join $wpdb->postmeta wpostmeta
    on wposts.ID = wpostmeta.post_id
    join $wpdn->postmeta l
    on wposts.ID = l.post_id
    and l.meta_key = '_artist_artist_last_name'
WHERE
(( wpostmeta.meta_key = '_artist_country' AND wpostmeta.meta_value = %s)
OR (wpostmeta.meta_key = '_artist_country_sub' AND wpostmeta.meta_value = %s) )
AND wposts.post_type = 'artists'
AND wposts.post_status = 'publish'
ORDER BY l.meta_value ASC
";
$myposts = $wpdb->get_results($wpdb->prepare( $querystr, $country_alt, $country_alt ), OBJECT);

Hope this helps.