mongodb-queries-01-count-by-order-status.json

// Count by order_status
db.orders.
  aggregate([{"$group" : 
                { "_id" : "$order_status", "status_count" : {"$sum" :1 }}
             }, 
             {"$project" : 
               { "order_status" : "$_id" , "status_count" : 1, "_id" : 0 }
             }])

mongodb-queries-02-revenue-for-eachorder-status.json

// Get revenue for each order
db.order_items.find({"order_item_order_id" : 2})   

db.order_items.
  aggregate([{"$group" : 
               { "_id" : "$order_item_order_id", "order_revenue" :{ "$sum" : "$order_item_subtotal" }}
             },
             {"$project" : 
               { "order_item_order_id" : "$_id", "order_revenue" : 1, "_id" : 0 }
             }])

mongodb-queries-03-filter-for-order-id.json

// Get revenue for order_id 2
db.order_items.
  aggregate([{ "$match" : {"order_item_order_id" : 2}},
             {"$group" : 
               { "_id" : "$order_item_order_id", "order_revenue" : {"$sum" : "$order_item_subtotal"}}
             },
             {"$project" : { "order_item_order_id": "$_id", "order_revenue" : 1, "_id" : 0 }
             }])