-- offset - is the number of rows forwarding from the current row from which to get the value. The default is 1. -- default - If the offset goes beyond the scope of ...

count(order_id) over (partition by month(order_date)) as orders_count_monthwise, sum(sales_amount) over (partition by month(order_date)) as sales_value_monthwise, sum ...

I want to design a query to compute some returns for stock data and in searching the 'SQL Server Books Online' I find a very small and not so helpful at all help section on the lead and lag functions.