Oracle 18c

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with table1(tran_id, user_id, start_date, end_date) as ( 
    select 1, 100, date '2018-06-01', date '2018-06-18' from dual union all 
    select 2, 100, date '2018-06-14', date '2018-06-14' from dual union all
    select 4, 100, date '2018-07-19', date '2018-07-19' from dual union all
    select 7, 101, date '2018-01-05', date '2018-01-06' from dual union all
    select 9, 101, date '2018-01-08', date '2018-01-08' from dual union all
    select 3, 101, date '2018-01-03', date '2018-01-03' from dual )
select rownum        as my_id,
       tran_id       as transidfrom,
       next_tran_id  as transidto,
       end_date      as transidfrom_end_date,
       next_end_date as transidto_start_date,
       datediff
  from (select tran_id,
               user_id,
               start_date,
               end_date,
               lead(tran_id) over (partition by user_id order by end_date) next_tran_id,
               lead(start_date) over (partition by user_id order by end_date) next_end_date,
               lead(start_date) over (partition by user_id order by end_date) - end_date datediff
          from table1)
 where datediff > 0;

MY_ID	TRANSIDFROM	TRANSIDTO	TRANSIDFROM_END_DATE	TRANSIDTO_START_DATE	DATEDIFF
1	1	4	18-JUN-18	19-JUL-18	31
2	3	7	03-JAN-18	05-JAN-18	2
3	7	9	06-JAN-18	08-JAN-18	2