python - Pymongo 聚合管道

Question

修订问题。将很快更新。

Answer 1

演示 - https://mongoplayground.net/p/ksay82IaGHs
按 TeacherID 分组和 TeacherID并获得组合的出现，$sort by occurrence按降序排列。

db.collection.aggregate([
  { $group: { _id: { TeacherID: "$TeacherID", StudentID: "$StudentID" }, occurrence: { $sum: 1 } } },
  { $sort: { "occurrence": -1 } }
]);

输出

[
  {
    "_id": {
      "StudentID": 2,
      "TeacherID": 212
    },
    "occurrence": 3
  },
  {
    "_id": {
      "StudentID": 4,
      "TeacherID": 223
    },
    "occurrence": 1
  }, .....
 ]

如果你想要最高记录
演示 - https://mongoplayground.net/p/zBsGdAOdYwy

  {
    "$limit": 1
  }

演示 - https://mongoplayground.net/p/G2KIVcjtYII
如果要检查特定的 TeacherID，请使用 $match