I am unable to retrive data from database in android from sqlite without php or any

I am doing a project where i need to retrieve data from sqlite database but it is not happening kindly help me through out.

my login code

package com.example.pallavi.myproject;

import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.text.InputType;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;


public class Login extends Activity{
    Intent i=null;

    EditText tv1,tv4;
    boolean flag=false;
    SQLiteDatabase db=null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);

        tv1 = (EditText) findViewById(R.id.phone2);
        tv4 = (EditText) findViewById(R.id.password2);
        db = openOrCreateDatabase("mydb", MODE_PRIVATE, null);



         }
    public void action(View v)
    {

                String mobile_no=tv1.getText().toString();
                String password=tv4.getText().toString();

              /*  if(mobile_no==null||mobile_no=="")
                {
                    show("Please Enter Correct mobile number.");
                }
                else if(password==null||password=="")
                {
                    show("Please Enter Correct Password.");
                }
                else*/
                {


                    show("Query is not executing");
                    String[] args={"null"};
                    Cursor c=db.rawQuery("select * from login where mobile_no='"+mobile_no+"'",args);
                    c.moveToFirst();
                    show("not going inside");

                    if(c.getCount()>0)
                    {
                        show("Success fully login");
                        i=new Intent(this,post.class);

                        db.close();
                        finish();
                    }
                    else
                        show("Wrong Password or Mobile number.");

                }

        }
    public void acc(View v)
    {
        if (v.getId()==R.id.button)
        {

            Intent i=new Intent(Login.this,MainActivity.class);
            startActivity(i);
        }
    }

    @Override
     protected void onActivityResult(int requestCode, int resultCode, Intent data) {

    }

    public void show(String str)
    {
        Toast.makeText(this, str, Toast.LENGTH_LONG).show();
    }

}

kindly check through it. I am trying to retreive data from db and check but it is not performing the operation.