mysql 时间向减写法

select *  from  (

  select  c.OrderNumber , 

  c.Name as equipmentName,  

  a.*, 

  d.Starttime, d.Endtime,

  ( select datediff(d.Starttime, d.Endtime)) as Lev  ,

  case ( select datediff(d.Starttime, d.Endtime))

  when ( select datediff(d.Starttime, d.Endtime)) <=10  then '紧急维修'

  when  10<( select datediff(d.Starttime, d.Endtime))<=30 then  '预计维修' 

  else '无需维修' end as  LevName 

  from  cloud_componentlist a   

  left join   

  cloud_equipmentcomponen b  on  a.Id= b.component 

  left join   cloud_equipment c on c.EquipmentId = b.EquipmentId 

  left join   (select * from cloud_componentrepairrecord  limit 0, 1 order by CreateDate desc  ) d  

  on d.Cloud_componentId= a.Id where  1=1   order by Lev desc  )  a  limit 0,10;