SQL Server 2017

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create table TABLE_A(
    Code FLOAT,
    DateIn datetime,
    dateOut datetime,
    Garage varchar(30) 
);

insert into Table_A (Code, DateIn, dateOut, Garage)
values 
  ('1','2018-06-07 00:00:00.000','2018-12-19 00:00:00.000','X'),
  ('2','2018-05-30 00:00:00.000','2018-12-19 00:00:00.000','Y'),
  ('3','2018-08-08 00:00:00.000','2018-11-18 00:00:00.000','Z'),
  ('4','2018-12-30 00:00:00.000','2018-12-30 00:00:00.000','Y'),
  ('5','2018-09-16 00:00:00.000','2018-10-19 00:00:00.000','Y'),
  ('6','2018-05-08 00:00:00.000','2018-08-28 00:00:00.000','Z'),
  ('7','2018-01-29 00:00:00.000','2018-07-31 00:00:00.000','Z'),
  ('8','2018-05-24 00:00:00.000','2018-09-10 00:00:00.000','X'),
  ('9','2018-05-02 00:00:00.000','2018-06-30 00:00:00.000','Y'),
  ('10','2018-07-05 00:00:00.000','2018-12-09 00:00:00.00','Z')
10 rows affected

with dates as (
      select convert(date, '2018-01-01') as dte, 1 as lev
      union all
      select dateadd(month, 1, dte), lev + 1
      from dates
      where lev < 12
     )
select year(d.dte), month(d.dte), s.*
from dates d cross apply
     (select sum(case when a.Garage = 'X' then 1 else 0 end) as x,
             sum(case when a.Garage = 'Y' then 1 else 0 end) as y,
             sum(case when a.Garage = 'Z' then 1 else 0 end) as z
      from table_a a
      where a.datein <= d.dte and a.dateout >= d.dte
     ) s


(No column name)
(No column name)
x
y
z


2018
1
null
null
null

2018
2
0
0
1

2018
3
0
0
1

2018
4
0
0
1

2018
5
0
0
1

2018
6
1
2
2

2018
7
2
1
2

2018
8
2
1
2

2018
9
2
1
2

2018
10
1
2
2

2018
11
1
1
2

2018
12
1
1
1


WITH MONTHS AS (SELECT 1 MNTHS
      UNION ALL
      SELECT 2
      UNION ALL
      SELECT 3
      UNION ALL
      SELECT 4
      UNION ALL
      SELECT 5
      UNION ALL
      SELECT 6
      UNION ALL
      SELECT 7
      UNION ALL
      SELECT 8
      UNION ALL
      SELECT 9
      UNION ALL
      SELECT 10
      UNION ALL
      SELECT 11
      UNION ALL
      SELECT 12),
      YEAR AS (SELECT 2018 YEAR)
SELECT YEAR,
       MNTHS,
       SUM(CASE WHEN Garage = 'X' THEN 1 ELSE 0 END) AS X,
       SUM(CASE WHEN Garage = 'Y' THEN 1 ELSE 0 END) AS Y,
       SUM(CASE WHEN Garage = 'Z' THEN 1 ELSE 0 END) AS Z
FROM (SELECT * FROM MONTHS M CROSS JOIN YEAR Y) YEARS
LEFT JOIN TABLE_A T ON YEARS.MNTHS = MONTH(T.DateIn)
                    AND YEARS.YEAR = YEAR(T.DateIn)
GROUP BY YEAR(DateIn),
MONTH(DateIn),
MNTHS,
YEAR
ORDER BY YEAR,
         MNTHS


YEAR
MNTHS
X
Y
Z


2018
1
0
0
1

2018
2
0
0
0

2018
3
0
0
0

2018
4
0
0
0

2018
5
1
2
1

2018
6
1
0
0

2018
7
0
0
1

2018
8
0
0
1

2018
9
0
1
0

2018
10
0
0
0

2018
11
0
0
0

2018
12
0
1
0
(No column name)	(No column name)	x	y	z
2018	1	null	null	null
2018	2	0	0	1
2018	3	0	0	1
2018	4	0	0	1
2018	5	0	0	1
2018	6	1	2	2
2018	7	2	1	2
2018	8	2	1	2
2018	9	2	1	2
2018	10	1	2	2
2018	11	1	1	2
2018	12	1	1	1