Use_case_of_lag_window_function

Suppose we have 3 columns in a table emp_no, salary, month

emp_no    salary    month
123       1000       jan
123       2000       feb
123       3000       march
So, output should look like:

emp_no    salary    month      diff
123       1000       jan       1000
123       2000       feb       1000
123       3000       march



select emp_no, 
       salary, 
       month,
       lag(salary) over (partition by emp_no order by month) - salary as diff_to_prev,
       lead(salary) over (partition by emp_no order by month) - salary as diff_to_next
from emp_table;