Query reference=FirebaseDatabase.getInstance().getReference().child("products").orderByChild("name").equalTo("iphon");
reference.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
String key=childSnapshot.getKey();
Log.i(TAG,key);
}
}