pass post ids to pre_get_posts query post__in function

add_action( ‘pre_get_posts’, ‘query_booked_posts’ );

function query_booked_posts( $query ) {
if ( $condition ) { //the condition

if ( is_home() && $query->is_main_query() )
$results = $wpdb->get_col($wpdb->prepare( “SELECT booked_id FROM $wpdb->userbooking WHERE userid = %d”,$current_user_id));

$query->set (‘post__in’, array($results)); // pass results (post ids) to post__in

return $query;
}

}

I want to let the function return the posts by the query->set with post ids post__in, But the function returns nothing.
Please help me. Thanks

Jason