db.sales.aggregate(
  [
    { $match : { "items.fruit":"banana" } },
    { $sort : { "date" : 1 } }
])

db.sales.aggregate(
   [
      {
         $unwind: "$items"
      },
      { $match: {
         "items.fruit" : "banana",
      }},
      {
        $group : {
           _id : { day: { $dayOfWeek: "$date" } },
           count: { $sum: "$items.quantity" }
        }
      },
      {
        $project: {
          dayOfWeek: "$_id.day",
          numberSold: "$count",
          _id:0
        }
      },
      {
        $sort: { "numberSold": 1 }
      }
   ]
)

db.sales.aggregate([
  {
     $unwind: "$items"
  },
  {
    $group : {
       _id : { day : { $dayOfWeek : "$date" } },
       items_sold : { $sum : "$items.quantity" },
       revenue: { $sum : { $multiply : [ "$items.quantity", "$items.price" ] } }
    }
  },
  {
    $project : {
      day : "$_id.day",
      revenue : 1,
      items_sold : 1,
      discount: {
        $cond : { if : { $lte : [ "$revenue", 250 ] }, then : 25, else : 0 }
      }
    }
  }
 ])

db.air_alliances.aggregate( [
   {
      $lookup : {
        from : "air_airlines",
        let : { constituents: "$airlines" },
        pipeline : [
          {
            $match : { $expr : { $in : [ "$name", "$$constituents" ] } }
            }
        ],
        as : "airlines"
      }
   },
   {
     $project : {
       "_id" : 0,
       "name" : 1,
       airlines : {
          $filter : {
            input : "$airlines",
            as : "airline",
            cond : { $eq: ["$$airline.country", "Canada"] }
          }
       }
     }
   }
])

db.runCommand({buildInfo: 1})

db.runCommand({collStats:"restaurants"})

db.records.createIndex( { score: 1 } )

db.restaurants.createIndex(
   { cuisine: 1, name: 1 },
   { partialFilterExpression: { rating: { $gt: 5 } } }
)