Oracle - Condition on a datetime - sql

Question

I am working on this DB that contains informations on shop orders in a plant. I am using this query that retrieves order data, using the closing date as condition. It extracts order that are closed in a time range of two weeks.
select order.id, order.end_date, material.id, material.description
from plant.order inner join plant.material
on order.material = material.id
where order.end_date <= to_date('26/10/2018 06:00:00', 'DD/MM/YYYY HH24:MI:SS')
where order.end_date <= to_date('12/10/2018 06:00:00', 'DD/MM/YYYY HH24:MI:SS')
Since the workday is divided in shifts (for example, the workday 26th October starts from the 26/10 6:00 and ends in 27/10 6:00 to cover the 24 hours), I need to manage this thing.
Is it possible to use a condition that checks if the hour is < 6, and if the condition is true, it writes the correct value in another column?
Or is there a better way to manage it?
order.id order.end_date material.id material.description
-------- -------------- ----------- --------------------
1 26/10/2018 05:00 1 Lorem Ipsum
2 26/10/2018 07:00 2 Lorem Ipsum
order.workday (new column)
-------------
25/10/2018
26/10/2018
In this case the order id 1 should result of date 25/10/2018, while order id 2 should result of date 26/10/2018.
I hope that I have been clear.
Thanks

Answer 1

You could simply use TRUNC(order.end_date - 6/24)
WITH t AS (
SELECT TO_DATE('26/10/2018 05:00' , 'dd/mm/yyyy hh24:mi') AS end_date FROM dual
UNION ALL SELECT TO_DATE('26/10/2018 07:00' , 'dd/mm/yyyy hh24:mi') AS end_date FROM dual)
SELECT end_date, TRUNC(end_date - 6/24)
from t;
+----------------------------------------+
|END_DATE |TRUNC(END_DATE-6/24)|
+----------------------------------------+
|26.10.2018 05:00:00|25.10.2018 |
|26.10.2018 07:00:00|26.10.2018 |
+----------------------------------------+

Answer 2

Try below using CASE WHEN
select
order.id,
order.end_date,
material.id,
material.description,
case when TO_CHAR (order.end_date, 'HH24:MI:SS')<'06:00:00' then order.end_date- interval '1' day else order.end_date end as workday
from plant.order inner join plant.material,
on order.material = material.id
where order.end_date <= to_date('26/10/2018 06:00:00', 'DD/MM/YYYY HH24:MI:SS')
where order.end_date <= to_date('12/10/2018 06:00:00', 'DD/MM/YYYY HH24:MI:SS')