mongodb排序规则不适用于使用facet阶段的insinde聚合

db.collection.aggregate([
  {
    $facet: {
      subset1: [
        {
          $match: { field1: "value1" }
        },
        {
          $group: {
            _id: "$field2",
            count: { $sum: 1 }
          }
        }
      ],
      subset2: [
        {
          $match: { field1: "value2" }
        },
        {
          $group: {
            _id: "$field2",
            count: { $sum: 1 }
          }
        }
      ]
    }
  },
  {
    $sort: { "subset1.count": -1 }
  }
])