Hi,

Do you need something like in this post:
http://stackoverflow.com/a/11396406/385377

Changes required in grid code …

$opt["sortname"] = 'ABS(diff)';
$g->set_options($opt);

// you can provide custom SQL query to display data
$g->select_command = " SELECT *, DATEDIFF(`invdate`, CURDATE()) AS diff FROM `invheader`";