Previous / Next Post navigation by Author

I needed to do something very similar on one of my own projects. This is what I came up with:

function get_prev_post_by_author($link="« %link", $title="%title") {
        global $wpdb, $post;
        $prev = $wpdb->get_row($wpdb->prepare("SELECT ID, post_title FROM $wpdb->posts WHERE post_type='post' AND post_status='publish' AND post_author='".$post->post_author."' AND post_date < '".$post->post_date."' ORDER BY post_date DESC LIMIT 1;"));
        if($prev) {
                $title = preg_replace('/%title/',$prev->post_title, $title);
                echo preg_replace('/%link/', '<a href="'.get_permalink($prev->ID).'" rel="prev">'.$title.'</a>', $link);
        }
}                               

function get_next_post_by_author($link="%link &raquo;", $title="%title") {
        global $wpdb, $post;
        $next = $wpdb->get_row($wpdb->prepare("SELECT ID, post_title FROM $wpdb->posts WHERE post_type='post' AND post_status='publish' AND post_author='".$post->post_author."' AND post_date > '".$post->post_date."' ORDER BY post_date ASC LIMIT 1;"));
        if($next) {
                $title = preg_replace('/%title/',$next->post_title, $title);
                echo preg_replace('/%link/', '<a href="'.get_permalink($next->ID).'" rel="next">'.$title.'</a>', $link);
        }
}

You should be able to drop this into your functions.php file and then use it like the next_post_link and prev_post_link functions, except that this does not have the two optional category parameters.

that’s fantastic, exactly the kind of idea i was looking for. thanks!

just wanna say this helped me too, thanks! ??

can someone help me, to make this work for post navigation by categories instead of author? would be great, because im pretty new in wordpress developing.
thanks
anna

i changed the code from above to this:

function get_prev_post_by_cat($link="? %link", $title="%title") {
        global $wpdb, $post;
		$offset = ($paged-1) * $postsperpage;

        $prev = $wpdb->get_row($wpdb->prepare("SELECT
wp_terms.name,
wp_posts.post_title,
wp_posts.post_date
FROM wp_posts
LEFT JOIN wp_term_relationships
ON wp_term_relationships.object_id = wp_posts.ID
LEFT JOIN wp_term_taxonomy
ON wp_term_taxonomy.term_taxonomy_id = wp_term_relationships.term_taxonomy_id
LEFT JOIN wp_terms
ON wp_terms.term_id = wp_term_taxonomy.term_id
WHERE wp_term_taxonomy.taxonomy = 'category'
ORDER BY wp_terms.name, wp_posts.post_date DESC LIMIT $offset;"));
        if($prev) {
                $title = preg_replace('/%title/',$prev->post_title, $title);
                echo preg_replace('/%link/', '<a href="'.get_permalink($prev->ID).'" rel="prev">'.$title.'</a>', $link);
        }
}                               

function get_next_post_by_cat($link="%link ?", $title="%title") {
        global $wpdb, $post;
		$offset = ($paged-1) * $postsperpage;
        $next = $wpdb->get_row($wpdb->prepare("SELECT
wp_terms.name,
wp_posts.post_title,
wp_posts.post_date
FROM wp_posts
LEFT JOIN wp_term_relationships
ON wp_term_relationships.object_id = wp_posts.ID
LEFT JOIN wp_term_taxonomy
ON wp_term_taxonomy.term_taxonomy_id = wp_term_relationships.term_taxonomy_id
LEFT JOIN wp_terms
ON wp_terms.term_id = wp_term_taxonomy.term_id
WHERE wp_term_taxonomy.taxonomy = 'category'
ORDER BY wp_terms.name, wp_posts.post_date ASC LIMIT $offset ;"));
        if($next) {
                $title = preg_replace('/%title/',$next->post_title, $title);
                echo preg_replace('/%link/', '<a href="'.get_permalink($next->ID).'" rel="next">'.$title.'</a>', $link);
        }
}

but i think i have to include an offset parameter somehow?

please help me ??

greetings
anna