mysql中 sql语句可以这样写：
select * , (to_days(curdate()) - to_days(`end_date`)) as date_diff from `tab` order by date_diff asc ;
laravel模型中，可以这样写:
StandingBook::selectRaw("* ,(to_days(curdate()) - to_days(`end_date`)) as date_diff")
->orderBy("date_diff","asc")
->paginate($limit)
->toArray();
