Aggregation

Code

Copydb.purchase_orders.insertMany(
     [
          {product: "toothbrush", total: 4.75, customer: "Mike"},
          {product: "guitar", total: 199.99, customer: "Tom"},
          {product: "milk", total: 11.33, customer: "Mike"},
          {product: "pizza", total: 8.50, customer: "Karen"},
          {product: "toothbrush", total: 4.75, customer: "Karen"},
          {product: "pizza", total: 4.75, customer: "Dave"}
          {product: "toothbrush", total: 4.75, customer: "Mike"},
     ]
)

// find out how many toothbrushes were sold
db.purchase_orders.count({product: "toothbrush"})

// Find list of all products sold
db.purchase_orders.distinct("product")

// Find the total amount of money spent by each customer
db.purchase_orders.aggregate(
     [
          {$match: {} },
          {$group: {_id: "$customer", total: { $sum: "$total"} } }
     ]
)

// Find how much has been spent on each product and sort it by price
db.purchase_orders.aggregate(
     [
          {$match: {} },
          {$group: {_id: "$product", total: { $sum: "$total"} } },
          {$sort: {total: -1}}
     ]
)

// Find how much money each customer has spent on toothbrushes and pizza
db.purchase_orders.aggregate(
     [
          {$match: {product: {$in: ["toothbrush", "pizza"]} } },
          {$group: {_id: "$product", total: { $sum: "$total"} } },
     ]
)

// https://docs.mongodb.com/manual/reference/operator/aggregation/
// Show the list of all pipeline operators