Firebird 3.0

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create table SHIFT_LOG_ENTRY (
  SHIFT_LOG_DET_ID integer,
  ENTRY_TIME timestamp
)


insert into SHIFT_LOG_ENTRY(SHIFT_LOG_DET_ID, ENTRY_TIME) values (1, timestamp'2019-09-19 16:13:00');
1 rows affected

insert into SHIFT_LOG_ENTRY(SHIFT_LOG_DET_ID, ENTRY_TIME) values (1, timestamp'2019-09-19 16:32:00');
1 rows affected

insert into SHIFT_LOG_ENTRY(SHIFT_LOG_DET_ID, ENTRY_TIME) values (1, timestamp'2019-09-19 16:45:00');
1 rows affected

select
  SHIFT_LOG_DET_ID,
  ENTRY_TIME,
  datediff(minute from ENTRY_TIME to NEXT_ENTRY_TIME) as DURATION
from (
  select 
    a.SHIFT_LOG_DET_ID,
    a.ENTRY_TIME, 
    (select min(ENTRY_TIME) 
     from SHIFT_LOG_ENTRY 
     where SHIFT_LOG_DET_ID = a.SHIFT_LOG_DET_ID
     and ENTRY_TIME > a.ENTRY_TIME) as NEXT_ENTRY_TIME
  from SHIFT_LOG_ENTRY a
) b


SHIFT_LOG_DET_ID
ENTRY_TIME
DURATION


1
2019-09-19 16:13:00
19

1
2019-09-19 16:32:00
13

1
2019-09-19 16:45:00
null




select
  SHIFT_LOG_DET_ID,
  ENTRY_TIME,
  datediff(minute from ENTRY_TIME to lead(ENTRY_TIME) over (partition by SHIFT_LOG_DET_ID order by ENTRY_TIME)) as DURATION
from SHIFT_LOG_ENTRY


SHIFT_LOG_DET_ID
ENTRY_TIME
DURATION


1
2019-09-19 16:13:00
19

1
2019-09-19 16:32:00
13

1
2019-09-19 16:45:00
null

SHIFT_LOG_DET_ID	ENTRY_TIME	DURATION
1	2019-09-19 16:13:00	19
1	2019-09-19 16:32:00	13
1	2019-09-19 16:45:00	null