check for logout status in oracle sql - sql

Question

I have written below query to retrieve the values,
select * from abc where status in ('login,'logout');
Status
Time
Login
2021-08-29 10:00:00
Logout
2021-08-29 10:30:00
Login
2021-08-29 11:00:00
In the table above, I have to check if the latest logout status is empty or present. But logout is not done yet.
I want to use IF condition to check if logout status is empty or present and it should use only the latest values. For example, the above query retrieves all values, but I want only the latest value ,that is
Login is at 2021-08-29 11:00:00 , but logout is not done yet.
I want only last record as output. Suppose if logout has been done,
Status
Time
Login
2021-08-29 10:00:00
Logout
2021-08-29 10:30:00
Login
2021-08-29 11:00:00
Logout
2021-08-29 11:30:00
Then I should get,
Status
Time
Login
2021-08-29 11:00:00
Logout
2021-08-29 11:30:00
as output

Answer 1

If the correct sequence is maintained by the logging application (Login before Logout and no consecutive duplicates of the same status), then you need to select the last two statuses and decide, whether to show the time of Logout (if it is the last), or not (if it is followed by Login status).
insert into t(status, time)
select 'Login', timestamp '2021-08-29 10:00:00' from dual union all
select 'Logout', timestamp '2021-08-29 10:30:00' from dual union all
select 'Login', timestamp '2021-08-29 11:00:00' from dual
create view v_test as
with last_ as (
select t.*
, row_number() over(partition by status order by time desc) as rn
/*There should be nothing after last logout*/
, lead(status) over(order by time) as next_status
from t
where status in ('Login', 'Logout')
)
select
status
/*
Show the time of the last status (regardless of its type),
And the time of the Login status if it's followed by Logout.
*/
, decode(next_status, 'Logout', time, null, time) as time
from last_
where rn = 1
select *
from v_test
STATUS | TIME
:----- | :------------------
Login | 2021-08-29 11:00:00
Logout | null
insert into t(status, time)
values('Logout', timestamp '2021-08-29 11:30:00')
select *
from v_test
STATUS | TIME
:----- | :------------------
Login | 2021-08-29 11:00:00
Logout | 2021-08-29 11:30:00
db<>fiddle here

Answer 2

The following approach uses window functions to determine the last login time and the logout time after the last login time
SELECT
status, time
FROM (
select
status,time ,
CASE
WHEN status='Login' AND
(time = MAX(time) OVER (PARTITION BY status)) THEN 1
ELSE 0
END as is_last_login,
CASE
WHEN status='Logout' AND
(time > MAX(CASE WHEN status='Login' THEN time END) OVER ()) THEN 1
ELSE 0
END as is_logout_after_last_login
from
abc
where
status in ('Login','Logout')
) t
WHERE
t.is_last_login=1 OR t.is_logout_after_last_login=1;
or
WITH last_login_time AS (
select max(time) last_login from abc where status='Login'
)
select
status,
time
from
abc
where
(
status='Login' AND time = (select last_login from last_login_time)
) OR
(
status='Logout' AND time > (select last_login from last_login_time)
)
Working Demo Db Fiddle
Edit 1
Left joining on a temporary table as shown in the example query below will also provide a null result for Logout if there is no logout entry as yet
WITH last_login_time AS (
select max(time) last_login from abc where status='Login'
),
login_logout_times AS (
select
status,
time
from
abc
where
(
status='Login' AND time = (select last_login from last_login_time)
) OR
(
status='Logout' AND time > (select last_login from last_login_time)
)
)
select
d.status,
l.time
from (
select 'Login' as status from dual
union all
select 'Logout' as status from dual
) d
left join login_logout_times l on l.status=d.status
Working Demo Db Fiddle
Let me know if this works for you.