SQL & PL/SQL

Hi All,

I am trying to subtract current row and 1 preceding row, which analytic function should I choose? (Opposite of sum)

select a.*, SUBTRACT(endpoint_number) over(order by endpoint_number rows between 1 preceding and current row) 
from user_histograms a where table_name = 'T' and column_name = 'YENI';

Regards

Charlie