Giving a query to my database and returning the result

So I put a function in my php function code which was

public function getName($name){
$result = mysql_query("SELECT * FROM 'users' WHERE 'name' = '$name' or trigger_error(mysql_error());

return "$result"; }

Edit: my question is how do I call this code in my android class so that I can put that result in an arraylist which is my ultimate goal.

I am trying to get all the names in that column and put them in an array list. And so in my activity android class i put this code.

 Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(Constants.BASE_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build();

    RequestInterface requestInterface = retrofit.create(RequestInterface.class);

    User user = new User();
    user.setName(name);
    user.setEmail(email);
    user.setPassword(password);

    usernames.add(name);
    ServerRequest request = new ServerRequest();
    request.setOperation(Constants.REGISTER_OPERATION);
    request.setUser(user);

    Call<ServerResponse> response = requestInterface.operation(request);

    response.enqueue(new Callback<ServerResponse>() {
        @Override
        public void onResponse(Call<ServerResponse> call, retrofit2.Response<ServerResponse> response) {

            ServerResponse resp = response.body();
            Snackbar.make(getView(), resp.getMessage(), Snackbar.LENGTH_LONG).show();
            progress.setVisibility(View.INVISIBLE);

        }

I am not sure if this is right, any help would be much appreciated!