How to check when a parameter was changed

Thanks to Sandeep Singh for providing this very useful information.

The following query will reveal any changes to a particular parameter:

select instance_number instance, snap_id, time, parameter_name, old_value, new_value 
from (
       select a.snap_id,to_char(end_interval_time,'DD-MON-YY HH24:MI') TIME, a.instance_number, parameter_name, value new_value,
       lag(parameter_name,1) over (partition by parameter_name, a.instance_number order by a.snap_id) old_pname,
       lag(value,1) over (partition by parameter_name, a.instance_number order by a.snap_id) old_value ,
       decode(substr(parameter_name,1,2),'__',2,1) calc_flag
from dba_hist_parameter a, dba_Hist_snapshot b , v$instance v
where a.snap_id=b.snap_id
and   a.instance_number=b.instance_number
and   parameter_name like nvl('&parameter_name',parameter_name)
and   a.instance_number like nvl('&instance_number',v.instance_number)
)
where
new_value != old_value
order by 1,2;

In my case the output was

INSTANCE	SNAP_ID	TIME	PARAMETER_NAME	OLD_VALUE	NEW_VALUE
1	52050	28-FEB-22 14:00	optimizer_adaptive_statistics	TRUE	FALSE