Weekly GMV and Repeat Buyers

Amazon's retail analytics team reports on fiscal weeks defined in calendar_weeks (week_start to week_end, both inclusive). An order belongs to the week that contains its order date; the time of day does not matter, so an order at 23:30 on week_end still belongs to that week. Only orders with status = 'completed' count. Every week in calendar_weeks must appear, with 0 for weeks that have no completed orders. Write an SQL query that returns week_start, weekly_gmv (the sum of gmv of completed orders) and repeat_buyers (the number of users with at least 2 completed orders in that week). Order the results by week_start ascending.