group by on the multiple inner join in postgres - sql

Question

i have 3 tables the first table "A" is the master table
id_grp|group_name |created_on |status|
------+--------------+-----------------------+------+
17|Teller |2022-09-09 16:00:44.842| 1|
18|Combined Group|2022-09-09 10:16:42.473| 1|
16|admnistrator |2022-09-08 10:11:14.313| 1|
Then i have another table table "b"
id_config|id_grp|id_utilis|
---------+------+---------+
159| 16| 1|
161| 16| 54|
164| 17| 55|
438| 17| 88|
166| 18| 39|
167| 18| 20|
439| 16| 89|
198| 18| 51|
Then i have the last table "C"
id_config|id_grp|id_pol|
---------+------+------+
46| 16| 7|
48| 17| 8|
51| 18| 8|
52| 18| 7|
84| 18| 9|
113| 17| 9|
but when i using group by with multiple join as follows
SELECT
a.id_grp,
a.group_name,
a.created_on,
a.status,
count(b.id_utilis) AS users,
count(c.id_pol) AS policy
FROM a
inner JOIN b on a.id_grp = b.id_grp
inner JOIN c on a.id_grp = c.id_grp
GROUP BY a.id_grp, a.group_name, a.created_on, a.status,
but i am getting wront result there both the count are creating matrix and multiplying each other
id_grp|group_name |created_on |status|users|policy|
------+--------------+-----------------------+------+-----+------+
17|Teller |2022-09-09 16:00:44.842| 1| 10| 10|
16|admnistrator |2022-09-08 10:11:14.313| 1| 3| 3|
18|Combined Group|2022-09-09 10:16:42.473| 1| 18| 18|

Answer 1

select *
from a
join (select id_grp, count(*) as users from b group by id_grp) b using(id_grp)
join (select id_grp, count(*) as policy from c group by id_grp) c using(id_grp)
id_grp
group_name
created_on
status
users
policy
17
Teller
2022-09-09 16:00:44
1
2
2
18
Combined Group
2022-09-09 10:16:42
1
3
3
16
admnistrator
2022-09-08 10:11:14
1
3
1
Fiddle