$match
$project
$group
$merge
$sort

--

[
   { $match: { quantity: 20 } },
   { $project: { _id: 0, amount: 0 } },
   { $merge : { into : "newCollection3" } }
]


[
   {
      $match:
      {
         'date': { $gte: new ISODate( '2020-01-30' ), $lt: new ISODate( '2022-01-30' ) }
      }
   },
   {
      $group:
      {
         _id: { $dateToString: { format: '%Y-%m-%d', date: '$date' } },
         totalOrderValue: { $sum: { $multiply: [ '$price', '$quantity' ] } },
         averageOrderQuantity: { $avg: '$quantity' }
      }
   },
   {
     $project: { _id:0 }
   },
   {
      $sort: { totalOrderValue: -1 }
   },
   { 
      $merge : { into : "result1" } 
   }
]

===========

[{
        $match: {
            infected_per_100k: {
                $lt: 1000
            }
        }
    }, {
        $lookup: {
            from: "gemeenten",
            localField: "gmcode",
            foreignField: "gemcode",
            as: "gemeente"
        }
    }, {
        $project: {
            _id: 0,
            date_unix: 0,
            gmcode: 0,
            date_of_insertion_unix: 0,
            gemeente: {
                _id: 0,
                vrCode: 0,
                gemcode: 0
            }
        }
    }, {
        $sort: {
            infected_per_100k: 1
        }
    }
]

=============
[
  {
   $lookup:
    {
      from: "corona",
      localField: "gemcode",
      foreignField: "gmcode",
      as: "corona"
    }
  },
  {
    $project:
    {
       _id : 0, vrCode:0, gemcode:0,
	   cccc: "$corona.infected"
      corona:
      {
        _id : 0, date_unix:0, gmcode:0, date_of_insertion_unix:0      
	  }
    }
  },
  {
    $sort:
    {
       "corona.infected": 1
    }
  }
]

==============

gemeenten
[
	{
		"_id": "621b8de80f55b62f30b118bb",
		"name": "Aa en Hunze",
		"vrCode": "VR03",
		"gemcode": "GM1680"
	},
	{
		"_id": "621b8de80f55b62f30b118bc",
		"name": "Aalsmeer",
		"vrCode": "VR13",
		"gemcode": "GM0358"
	},
	....
]

corona
[
	{
		"_id": "621b8b70e82fd20baf55255c",
		"date_unix": 1645833600,
		"gmcode": "GM0014",
		"infected_per_100k": 373,
		"infected": 870,
		"date_of_insertion_unix": 1645881053
	},
	{
		"_id": "621b8b70e82fd20baf55255d",
		"date_unix": 1645833600,
		"gmcode": "GM0034",
		"infected_per_100k": 101.5,
		"infected": 218,
		"date_of_insertion_unix": 1645881053
	},
    .....
]


-------------------
db.gemeenten.aggregate(
[
	{
        $lookup: 
		{
            from: "corona",
            localField: "gemcode",
            foreignField: "gmcode",
            as: "corona"
        }
    }, 
	{
        $project: 
		{
            _id: 0,
            Name: "$name",
            "infected": 
			{
                $arrayElemAt: ["$corona.infected", 0]
            },
            "infected_per_100k": 
			{
                $arrayElemAt: ["$corona.infected_per_100k", 0]
            }
        }
    }, 
	 
])

===========
db.corona.aggregate(
[
  {
   $lookup:
    {
      from: 'gemeenten',
      localField: 'gmcode',
      foreignField: 'gemcode',
      as: 'corona_gemeenten'
    }
  },
  {
	$unwind: '$corona_gemeenten'
  },
  {
    $project:
    {
	_id:0,
	Name: '$corona_gemeenten.name',
	infected_per_100k:1
	infected: 1,
    }
  },
  {
    $sort:
    {
      infected_per_100k:-1
    }
  }
])


{
  name: "ShowCorona",
  DbName: "test",
  ColName: "corona",
  query:
"[
  {
   $lookup:
    {
      from: 'gemeenten',
      localField: 'gmcode',
      foreignField: 'gemcode',
      as: 'corona_gemeenten'
    }
  },
  {
	$unwind: '$corona_gemeenten'
  },
  {
    $project:
    {
	_id:0,
	Name: '$corona_gemeenten.name',
	infected_per_100k:1
	infected: 1,
    }
  },
  {
    $sort:
    {
      infected_per_100k:-1
    }
  }
]"
}