https://developers.weixin.qq.com/miniprogram/dev/wxcloud/reference-sdk-api/database/aggregate/Aggregate.group.html

{
  "_id": {
    "region": "asia",
    "maxScore": 100
  },
  "totalCoins": 100
}

其中totalCoins应该是40，不应该是100。因为符合条件的记录只有这1条：

{
  _id: "4",
  alias: "john",
  region: "asia",
  scores: [30, 60, 100, 90],
  coins: 40
}