SQL Server 2019

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create table [Users]
(
   [Id] int,
   [Name] nvarchar(50),
   [Email] nvarchar(50)
)

create table [Transactions]
(
   [Id] int,
   [UserId] int,
   [Credit] decimal(18,2),
   [Debit] decimal(18,2),
   [Description] nvarchar(100),
   [DateAdded] datetime
)
insert into [Users](Id, Name, Email) values(1,'user1','user1@example.com');
insert into [Users](Id, Name, Email) values(2,'user2','user2@example.com');
insert into [Users](Id, Name, Email) values(3,'user3','user3@example.com');
insert into [Users](Id, Name, Email) values(4,'user4','user4@example.com');
insert into [Users](Id, Name, Email) values(5,'user5','user5@example.com');

insert into [Transactions](Id, UserId, Credit, Debit, Description, DateAdded) values(1, 1, 10.00, 0.00, 'Add-Cash', '2020-05-19 00:00:00.000');
insert into [Transactions](Id, UserId, Credit, Debit, Description, DateAdded) values(2, 2, 0.00, 15.00, 'Buy Course XYZ', '2020-04-01 00:00:00.000');
insert into [Transactions](Id, UserId, Credit, Debit, Description, DateAdded) values(3, 3, 0.00, 20.00, 'Buy Course ABC', '2020-05-15 00:00:00.000');
insert into [Transactions](Id, UserId, Credit, Debit, Description, DateAdded) values(4, 4, 0.00, 15.00, 'But Course IJK', '2020-05-01 00:00:00.000');
9 rows affected

select u.*
from users u
where not exists (select 1
                  from transactions t
                  where t.userid = u.id and
                        t.dateadded > dateadd(day, -30, getdate())
                 )


Id
Name
Email


1
user1
user1@example.com

2
user2
user2@example.com

3
user3
user3@example.com

4
user4
user4@example.com

5
user5
user5@example.com

Id	Name	Email
1	user1	user1@example.com
2	user2	user2@example.com
3	user3	user3@example.com
4	user4	user4@example.com
5	user5	user5@example.com