SQL Server 2017

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create table tablename (date_details DATE, account_id varchar(2), user_id varchar(2));

insert into tablename(date_details, account_id, user_id) values
('2021-01-01','U1','A1'),
('2021-01-01','U1','A2'),
('2021-01-01','U1','A3'),
('2021-01-01','U1','A4'),
('2021-02-01','U1','A1'),
('2021-02-01','U1','A2'),
('2021-02-01','U1','A3'),
('2021-02-01','U1','A4'),
('2021-02-01','U1','A5'),

('2021-01-01','U2','A1'),
('2021-01-01','U2','A2'),
('2021-01-01','U2','A3'),
('2021-02-01','U2','A1'),
('2021-02-01','U2','A2')
14 rows affected

select * from tablename


date_details
account_id
user_id


2021-01-01
U1
A1

2021-01-01
U1
A2

2021-01-01
U1
A3

2021-01-01
U1
A4

2021-02-01
U1
A1

2021-02-01
U1
A2

2021-02-01
U1
A3

2021-02-01
U1
A4

2021-02-01
U1
A5

2021-01-01
U2
A1

2021-01-01
U2
A2

2021-01-01
U2
A3

2021-02-01
U2
A1

2021-02-01
U2
A2


with cte as (
select account_id, count(distinct(user_id)) as unique_user, MONTH(date_details) as user_month from tablename
group by account_id, MONTH(date_details)
)

select a.account_id,month_2,month_1,
cast((month_2/month_1)as float) as growth  from 
(select account_id, unique_user as month_1
from cte where user_month = 1)a
left join
(select account_id, unique_user as month_2
from cte where user_month = 2)b
on (a.account_id = b.account_id)


account_id
month_2
month_1
growth


U1
5
4
1

U2
2
3
0

date_details	account_id	user_id
2021-01-01	U1	A1
2021-01-01	U1	A2
2021-01-01	U1	A3
2021-01-01	U1	A4
2021-02-01	U1	A1
2021-02-01	U1	A2
2021-02-01	U1	A3
2021-02-01	U1	A4
2021-02-01	U1	A5
2021-01-01	U2	A1
2021-01-01	U2	A2
2021-01-01	U2	A3
2021-02-01	U2	A1
2021-02-01	U2	A2