SQL Server 2017

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CREATE TABLE tablename
    ([Process_name] varchar(5), [Start] datetime, [End] datetime)
;
    
INSERT INTO tablename
    ([Process_name], [Start], [End])
VALUES
    ('A', '2019-01-01 14:10:00', '2019-01-01 14:55:00'),
    ('B', '2019-01-01 14:20:00', '2019-01-01 16:30:00'),
    ('C', '2019-01-01 15:05:00', '2019-01-01 15:10:00')
;
3 rows affected

with cte as (
  select 0 as hour
  union all
  select hour + 1 
  from cte 
  where hour < 23 
)
select c.hour Hour, count(*) ProcessQount 
from cte c inner join tablename t
on c.hour between datepart(hh, t.[Start]) and datepart(hh, t.[End])
group by c.hour


Hour
ProcessQount


14
2

15
2

16
1


with cte as (
  select 0 as hour
  union all
  select hour + 1 
  from cte 
  where hour < 23 
)
select c.hour Hour, count([Process_name]) ProcessQount 
from cte c left join tablename t
on c.hour between datepart(hh, t.[Start]) and datepart(hh, t.[End])
group by c.hour


Hour
ProcessQount


0
0

1
0

2
0

3
0

4
0

5
0

6
0

7
0

8
0

9
0

10
0

11
0

12
0

13
0

14
2

15
2

16
1

17
0

18
0

19
0

20
0

21
0

22
0

23
0


Warning: Null value is eliminated by an aggregate or other SET operation.

Hour	ProcessQount
0	0
1	0
2	0
3	0
4	0
5	0
6	0
7	0
8	0
9	0
10	0
11	0
12	0
13	0
14	2
15	2
16	1
17	0
18	0
19	0
20	0
21	0
22	0
23	0

Hour	ProcessQount
0	0
1	0
2	0
3	0
4	0
5	0
6	0
7	0
8	0
9	0
10	0
11	0
12	0
13	0
14	2
15	2
16	1
17	0
18	0
19	0
20	0
21	0
22	0
23	0

Hour	ProcessQount
0	0
1	0
2	0
3	0
4	0
5	0
6	0
7	0
8	0
9	0
10	0
11	0
12	0
13	0
14	2
15	2
16	1
17	0
18	0
19	0
20	0
21	0
22	0
23	0