您需要将索引添加到Firebase数据库安全规则中.我建议阅读有关安全规则的Firebase文档，尤其是部分.

You'll need to add an index to your Firebase Database security rules. I recommend reading the Firebase documentation on security rules, specifically the section on indexes.

文档中的第一个示例:

{
  "rules": {
    "dinosaurs": {
      ".indexOn": ["height", "length"]
    }
  }
}

修改为您的数据结构，看起来像这样:

Modified to your data structure, it'll look something like this:

{
  "rules": {
    "divisions": {
      ".indexOn": "index_num"
    }
  }
}