Pagination with custom SQL query

I have my own SQL string to select Custom Post Type posts with specific WHERE clause. I’ve used the offset and limit to return appropriate posts depending on a page being displayed. That’s working fine.

Now, I would like to make previous_posts_link() and next_posts_link() functions work. They both are called from get_posts_nav_link which uses global $wp_query.

Is there a way I can re-assign global $wp_query with my SQL string or $wpdb->get_results results or anything else? So the native previous_posts_link() and next_posts_link() WP functions would work.

If not, how can I reproduce the prev and next post link functions?

I would really appreciate any help and advice! I’m totally stuck with this.
Thanks 🙂

NOTE: I have just noticed that previous_posts_link() is working correctly on all the pages, but no idea why and in this case, why next_posts_link doesn’t work :S

Here is the code:

$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
$post_per_page = intval(get_query_var('posts_per_page'));
$offset = ($paged - 1)*$post_per_page;

$sql = "
SELECT SQL_CALC_FOUND_ROWS  wp_posts.*, wp_postmeta.* 
FROM wp_posts 
INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id)
INNER JOIN wp_postmeta AS mt1 ON (wp_posts.ID = mt1.post_id) 
WHERE 1=1  
    AND wp_posts.post_type="movie" 
    AND (wp_posts.post_status="publish" OR wp_posts.post_status="private") 
    AND ((wp_postmeta.meta_key = '_expiry_date' AND CAST(wp_postmeta.meta_value AS DATE) >= '".$current_date."') 
        OR (mt1.meta_key = '_expiry_date' AND CAST(mt1.meta_value AS CHAR) = ''))
GROUP BY wp_posts.ID 
ORDER BY wp_posts.post_date DESC
LIMIT ".$offset.", ".$post_per_page;

$movies_all_current = $wpdb->get_results( $sql, OBJECT);

if($movies_all_current) {
global $post;

//loop
foreach( $movies_all_current as $key=>$post ) {
    setup_postdata($post);
    //display each post
    //...
} //end foreach ?>

    //navigation
<div class="navigation">
    <div class="previous panel"><?php previous_posts_link('&laquo; newer') ?></div>
    <div class="next panel"><?php next_posts_link('older &raquo;') ?></div>
</div>
}

Ok, I got there at the end. I couldn’t use WP_Query class as I really needed to have my own pretty big and complex SQL. Here is what I ended up having:

In functions.php I have my custom SQL and logic for counting the values needed for the WP pagination logic:

function vacancies_current( ){
    global $wpdb, $paged, $max_num_pages, $current_date;

    $paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
    $post_per_page = intval(get_query_var('posts_per_page'));
    $offset = ($paged - 1)*$post_per_page;

    /* Custom sql here. I left out the important bits and deleted the body 
     as it will be specific when you have your own. */
    $sql = "
        SELECT SQL_CALC_FOUND_ROWS  {$wpdb->posts}.*
        FROM {$wpdb->posts}
        ....
        GROUP BY {$wpdb->posts}.ID 
        ORDER BY {$wpdb->posts}.post_date DESC
        LIMIT ".$offset.", ".$post_per_page."; ";   

    $sql_result = $wpdb->get_results( $sql, OBJECT);

    /* Determine the total of results found to calculate the max_num_pages
     for next_posts_link navigation */
    $sql_posts_total = $wpdb->get_var( "SELECT FOUND_ROWS();" );
    $max_num_pages = ceil($sql_posts_total / $post_per_page);

    return $sql_result;
}

Then in my template file I’d have:

<?php 
    $vacancies_current = vacancies_current();
    /*followed by a standart loop to display your results */ 
 ?>
<div class="navigation">
    <div class="previous panel"><?php previous_posts_link('&laquo; previous vacancies',$max_num_pages) ?></div>
    <div class="next panel"><?php next_posts_link('more vacancies &raquo;',$max_num_pages) ?></div>
</div>

The trick was in supplying previous_posts_link() and next_posts_link the $max_num_pages value and obviously in calculating it correctly.

This works very well. Hope it will help someone 🙂

Dasha