Do you have a Fiscal Calendar table to join with your base table? If not, Join your base table with SYS_CALENDAR.CALENDAR table to get the week_of_Calendar field for each DATE in your table. Now having the week numbers in your result set , use the sum function and group by week_of_calendar.
Something like this:
Select A.Week_No, SUM( A.sales_Amt) From ( Select Date As Sales_Date, Sales As Sales_Amt, Price As Price, Week_of_Calendar As Week_No From your_table, SYS_CALENDAR.CALENDAR Where your_table.Date=SYS_CALENDAR.CALENDAR.Calendar_Date ) A Group By 1