SQL: combine case and number to date conversion - sql

Question

I want to do a sql statement which calculates in one table the substraction of 2 Date values. If the value is negative I just want to show it as the 0 value.
The number value is the number of seconds a payment is in a current state.
I convert it with a trick to a time value(Date type).
My current code is
SELECT
max(CASE WHEN t1.time_event < SYSDATE and t2.time_event > SYSDATE THEN to_char(to_date(max(round(SYSDATE - t1.time_event) * 24 * 60 * 60)),'ssssss'),'hh24:mi:ss') else to_char(to_date(0)) END) as "current_age"
from tbl_dummyfeed t1 join tbl_dummyfeed t2 on t1.payment_Id = t2.payment_id
where t1.event = 'accepted' and t2.event = 'enriched');

Answer 1

You could use a similar date 'trick', which is to add the fractional-days difference to a nominal date which has the time portion as midnight - you could use a fixed date, or trunc(sysdate), as long as the time ends up as midnight - without having to multiply by 24*60*60. (Your to_date() solution does the same thing implicitly, effectively adding the number of seconds to midnight on the first day of the current month; but this might be a little clearer). But you can also move the case clauses into the where filter
select to_char(date '1970-01-01'
+ nvl(max(sysdate - t1.time_event), 0), 'HH24:MI:SS') as "current_age"
from tbl_dummyfeed t1
join tbl_dummyfeed t2
on t1.trax_id = t2.trax_id
where t1.event = 'accepted'
and t1.time_event < sysdate
and t2.event = 'enriched'
and t2.time_event > sysdate;
You could also use an analytic approach so you only have to hit the table once, with a subquery that pairs up each 'enriched' time with the previous 'accepted' time for that ID, and which you then filter against the current time:
select to_char(date '1970-01-01'
+ nvl(max(sysdate - time_accepted), 0), 'HH24:MI:SS') as "current_age"
from (
select last_value(case when event = 'accepted' then time_event end ignore nulls)
over (partition by trax_id order by time_event) as time_accepted,
case when event = 'enriched' then time_event end as time_enriched
from tbl_dummyfeed
)
where time_accepted < sysdate
and time_enriched > sysdate;

Answer 2

This works, only the conversion to time hh24:mi:ss still needs to happen.
SELECT max(CASE WHEN t1.time_event < SYSDATE and t2.time_event > SYSDATE THEN round((SYSDATE - t1.time_event) * 24 * 60 * 60) else 0 END) as "current_age"
from tbl_dummyfeed t1 join tbl_dummyfeed t2 on t1.payment_id= t2.payment_id
where t1.event = 'accepted' and t2.event = 'enriched';
When I add the conversion to hh24:mm:ss The solution looks like this
SELECT to_char(to_date(max(CASE WHEN t1.time_event < SYSDATE and t2.time_event > SYSDATE THEN round((SYSDATE - t1.time_event) * 24 * 60
* 60) else 0 END),'sssss'),'hh24:mi:ss') as "current_age" from tbl_dummyfeed t1 join tbl_dummyfeed t2 on t1.trax_Id = t2.trax_id where t1.event = 'accepted' and t2.event = 'enriched';
This is the only good solution for my question. Hope this helps people.