MS SQL SERVER 2014: Get Number of Days Between Occurrences, Sql Server

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create table t (id int, employeeid int, dateofoccurence date)
insert into t values 
 (1,999999,'2017-02-14')
,(2,999999,'2017-03-02')
,(3,999999,'2017-03-23')
,(4,999999,'2017-05-10')

select 
        id
      , range = concat(
          convert(char(10),dateofoccurence,120)
        , ' to '
        , convert(char(10),isnull(lead(dateofoccurence) over (partition by employeeid order by dateofoccurence),getdate()),120)
      )
      , days = concat(
          datediff(
             day
           , dateofoccurence
           , isnull(lead(dateofoccurence) over (partition by employeeid order by dateofoccurence),getdate())
          )
          - case when lag(dateofoccurence) over (partition by employeeid order by dateofoccurence) is null
                 then 0
                 else 1
                 end
        , ' days')
    from t
    
/* ------ */ 
/* 
select 
    id
  , range = concat(
      convert(char(10),dateofoccurence,120)
    , ' to '
    , convert(char(10),isnull(lead(dateofoccurence) over (partition by employeeid order by dateofoccurence),getdate()),120)
  )
  , days = concat(
      datediff(
         day
       , dateofoccurence
       , isnull(lead(dateofoccurence) over (partition by employeeid order by dateofoccurence),getdate())
      )
    , ' days')
from t
--*/

View schema
Execution time: 0,02 sec, rows selected: 8, rows affected: 4, absolute service time: 0,16 sec