Oracle SQL to calculate value based on previous row value

Oracle database allows you to use SQL to calculate value based on the values of the previous row in a query result set. Use LAG and LEAD analytic function to calculate based on previous rows values.

Usage:
Both functions have the same usage, as shown below.
LAG (value_expression [,offset] [,default]) OVER ([query_partition_clause] order_by_clause)
LEAD (value_expression [,offset] [,default]) OVER ([query_partition_clause] order_by_clause)

Description:
value_expression - Can be a column or a built-in function, except for other analytic functions.
offset - The number of rows preceeding/following the current row, from which the data is to be retrieved. The default value is 1.
default - The value returned if the offset is outside the scope of the window. The default value is NULL.

Example:

select salary,lag(salary+300,1,0) over (order by salary) as new_sal,lag(salary+200,2,0) over (order by salary) as new_sal2 from employees;