Sortable columns

/*-----------------------------------------------------------------------------------*/
/* Sortable columns for admin knowledge base section
/*-----------------------------------------------------------------------------------*/

// Register the new columns as sortable
function kbcategory_column_register_sortable( $columns ) {
$columns['meta_views'] = 'Views';
$columns['taxonomy_category'] = 'kbcategory';
$columns['taxonomy_related_products'] = 'relatedproducts';

return $columns;
}
add_filter( 'manage_edit-knowledge-base_sortable_columns', 'kbcategory_column_register_sortable' );

// Tell Wordpress how to sort the new column 'Views'
function views_column_orderby( $vars ) {
	if ( isset( $vars['orderby'] ) && 'Views' == $vars['orderby'] ) {
		$vars = array_merge( $vars, array(
			'meta_key' => 'Views',
			'orderby' => 'meta_value_num'
		) );
	}

	return $vars;
}
add_filter( 'request', 'views_column_orderby' );

// Tell Wordpress how to sort the new column 'Category'
function kbcategory_clauses( $clauses, $wp_query ) {
	global $wpdb;

	if ( isset( $wp_query->query['orderby'] ) && 'kbcategory' == $wp_query->query['orderby'] ) {

		$clauses['join'] .= <<<SQL
LEFT OUTER JOIN {$wpdb->term_relationships} ON {$wpdb->posts}.ID={$wpdb->term_relationships}.object_id
LEFT OUTER JOIN {$wpdb->term_taxonomy} USING (term_taxonomy_id)
LEFT OUTER JOIN {$wpdb->terms} USING (term_id)
SQL;

		$clauses['where'] .= " AND (taxonomy = 'kbcategory' OR taxonomy IS NULL)";
		$clauses['groupby'] = "object_id";
		$clauses['orderby']  = "GROUP_CONCAT({$wpdb->terms}.name ORDER BY name ASC) ";
		$clauses['orderby'] .= ( 'ASC' == strtoupper( $wp_query->get('order') ) ) ? 'ASC' : 'DESC';
	}

	return $clauses;
}
add_filter( 'posts_clauses', 'kbcategory_clauses', 10, 2 );

// Tell Wordpress how to sort the new column 'Related Products'
function relatedproducts_clauses( $clauses, $wp_query ) {
	global $wpdb;

	if ( isset( $wp_query->query['orderby'] ) && 'relatedproducts' == $wp_query->query['orderby'] ) {

		$clauses['join'] .= <<<SQL
LEFT OUTER JOIN {$wpdb->term_relationships} ON {$wpdb->posts}.ID={$wpdb->term_relationships}.object_id
LEFT OUTER JOIN {$wpdb->term_taxonomy} USING (term_taxonomy_id)
LEFT OUTER JOIN {$wpdb->terms} USING (term_id)
SQL;

		$clauses['where'] .= " AND (taxonomy = 'relatedproducts' OR taxonomy IS NULL)";
		$clauses['groupby'] = "object_id";
		$clauses['orderby']  = "GROUP_CONCAT({$wpdb->terms}.name ORDER BY name ASC) ";
		$clauses['orderby'] .= ( 'ASC' == strtoupper( $wp_query->get('order') ) ) ? 'ASC' : 'DESC';
	}

	return $clauses;
}
add_filter( 'posts_clauses', 'relatedproducts_clauses', 10, 2 );