Query monitoring changes in the field

I need to program a query where I can see the changes that certain fields have undergone in a certain date period. Example: From the CAM_CONCEN table bring those records where the ACCOUNT_NUMBER undergoes a modification in the CONCTACT field in a period of 6 months before the date. I would be grateful if you can guide me.

Answer

You can use LAG() to peek at the previous row of a particular subset of rows (the same account in this case).

For example:

select *
from (
  select c.*,
    lag(contact) over(partition by account_number
                      order by change_date) as prev_contact
  from cam_concen c
) x
where contact <> prev_contact