Update previous rows based on another row - sql-server

Question

I have a question and i need to update the empty rows based on the rows with value
In this case, i need to update the hours, mins and secs based on every 4th row
For ex: rownum 4 has 8hours, 1mins, 9 sec.
So, my update to previous row should be 8hrs, 1min, 6 sec from rownum 1, then, for rownum 5 it should continue the same procedure
See rownum 8 has 8hours, 1mins, 13 sec.
The previous 3 rows should be 8hrs, 1min, 10 sec from rownum 5
How to have this in a loop or with partition by or any suggestion in SQL server.

Answer 1

You can do this with window functions and converting your hours, minutes and seconds to a time value. Converting to a tim is important to make sure you wrap around the appropriate time boundaries and don't end up with 61 seconds in a minute etc.
Depending on the data and your real world environment you will probably need to add the Flight and maybe some other columns into the partition bys to ensure you are working correctly scoped windows of data.
Query
declare #t table(rn int,timeframe int,h int,m int,s int);
insert into #t values
(1,1,null,null,null)
,(2,1,null,null,null)
,(3,1,null,null,null)
,(4,1,23,59,45)
,(5,2,null,null,null)
,(6,2,null,null,null)
,(7,2,null,null,null)
,(8,2,23,59,49)
,(9,3,null,null,null)
,(10,3,null,null,null)
,(11,3,null,null,null)
,(12,3,23,59,53)
,(13,4,null,null,null)
,(14,4,null,null,null)
,(15,4,null,null,null)
,(16,4,23,59,57)
,(17,5,null,null,null)
,(18,5,null,null,null)
,(19,5,null,null,null)
,(20,5,0,0,1)
,(21,6,null,null,null)
,(22,6,null,null,null)
,(23,6,null,null,null)
,(24,6,0,0,5)
;
with d as
(
select rn
,timeframe
,dateadd(second
,rn - max(rn) over (partition by timeframe)
,max(timefromparts(h,m,s,0,0)) over (partition by timeframe)
) as t
from #t
)
select rn
,timeframe
,datepart(hour,t) as h
,datepart(minute,t) as m
,datepart(second,t) as s
from d
order by rn;
Output
rn
timeframe
h
m
s
1
1
23
59
42
2
1
23
59
43
3
1
23
59
44
4
1
23
59
45
5
2
23
59
46
6
2
23
59
47
7
2
23
59
48
8
2
23
59
49
9
3
23
59
50
10
3
23
59
51
11
3
23
59
52
12
3
23
59
53
13
4
23
59
54
14
4
23
59
55
15
4
23
59
56
16
4
23
59
57
17
5
23
59
58
18
5
23
59
59
19
5
0
0
0
20
5
0
0
1
21
6
0
0
2
22
6
0
0
3
23
6
0
0
4
24
6
0
0
5