Firebase查询orderByChild

{
  "users": {
    "user1": {
      "name": "Alice",
      "age": 30
    },
    "user2": {
      "name": "Bob",
      "age": 25
    },
    "user3": {
      "name": "Charlie",
      "age": 35
    }
  }
}

var ref = firebase.database().ref("users");
ref.orderByChild("age").on("value", function(snapshot) {
  snapshot.forEach(function(childSnapshot) {
    var key = childSnapshot.key;
    var childData = childSnapshot.val();
    console.log(key, childData);
  });
});

var ref = firebase.database().ref("users");
ref.orderByChild("age").equalTo(30).on("value", function(snapshot) {
  snapshot.forEach(function(childSnapshot) {
    var key = childSnapshot.key;
    var childData = childSnapshot.val();
    console.log(key, childData);
  });
});

var ref = firebase.database().ref("users");
ref.orderByChild("age").startAt(25).endAt(35).on("value", function(snapshot) {
  snapshot.forEach(function(childSnapshot) {
    var key = childSnapshot.key;
    var childData = childSnapshot.val();
    console.log(key, childData);
  });
});

var ref = firebase.database().ref("users");
ref.orderByChild("age").limitToLast(2).on("value", function(snapshot) {
  snapshot.forEach(function(childSnapshot) {
    var key = childSnapshot.key;
    var childData = childSnapshot.val();
    console.log(key, childData);
  });
});

{   "rules": {     ".read": "auth != null",     ".write": "auth != null",     "users": {       ".indexOn": ["age"]     }   } }