Oracle SQL closest date to given date

i have a table with a column for categories, date and price. Like this:

group 1  - 03.03.2019 - 5.00
group 1  - 03.02.2018 - 4.00
group 2  - 05.05.2019 - 2.25
group 2  - 05.05.2018 - 1.00

So there are (almost) always two dates per group with two different prices. Now i need to write an SQL Statement to get the closest date per group to a given date(f.e. 05.05.2019). Group 1 has two dates an the SQL statement needs to Select one of them which is the closest to the given date. This need to happen for all of the groups.

I tried it for a couple of hours but i am stuck. Thanks for ur help

Answer

Here is one option using not exists:

select t.*
from mytable t
where not exists (
    select 1
    from mytable t1
    where 
        t1.category = t.category 
        and greatest(t1.date, date '2019-05-05') - least(t1.date, date '2019-05-05')
            < greatest(t.date, date '2019-05-05') - least(t.date, date '2019-05-05')
)

This gives you the “closest” record to 2019-05-05 for each group (whether before or after).

If, for example, you want the closest record before 2019-05-05, that’s a bit simpler:

select t.*
from mytable t
where 
    t.date <= date '2019-05-05'
    and not exists (
        select 1
        from mytable t1
        where t1.category = t.category and t1.date <= date '2019-05-05' and t1.date > t.date
    )