Retrieve multiple filters in Firebase [Swift]

问题

Is there a way to quickly pull all the userId that has the same username? For example, if userId_002 also had the username "sean", can I quickly retrieve ["userId_001","userId_002"]? I appreciate any help!

I'm trying this but doesn't work:

    let results = Database.database().reference().child("usernames").queryOrdered(byChild: "username").queryEqual(toValue: "sean")
    
        results.observeSingleEvent(of: .value, with: { (snapshot) in
        
            for child in snapshot.children {

                let value = child as! DataSnapshot
                let key = value?["userId"] as? String ?? ""
                self.array.append(key)
            }
        }
    })

来源：https://stackoverflow.com/questions/65053999/retrieve-multiple-filters-in-firebase-swift