如何构建按平均值排序的MongoDB管道

db.collection.aggregate([
  {
    $group: {
      _id: null,
      average: { $avg: "$field1" }
    }
  }
])

db.collection.aggregate([
  {
    $group: {
      _id: null,
      average: { $avg: "$field1" }
    }
  },
  {
    $sort: { average: 1 }
  }
])

db.collection.aggregate([
  {
    $group: {
      _id: null,
      average: { $avg: "$field1" }
    }
  },
  {
    $sort: { average: -1 }
  }
])