How to display alertDialog in an activity when sqlite database is empty

I would like to display an alertDialog when there is no data stored in my database.However what i have tried seems not to achieve the desired goal as the alert dialog is not called when the database is empty.

Here is how i check for the existance of tables in my database:

public boolean checkForTables() {
        boolean hasTables = false;
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery("SELECT COUNT(*)FROM" + CONTACTS_TABLE_NAME, null);
        if (cursor != null && cursor.getCount() > 0) {
            hasTables = true;
            cursor.close();
        }
        return hasTables;
    }

And in my activity onCreate:

if (myDb.checkForTables()) {
            showTable();
            btn.setVisibility(View.VISIBLE);
        } else {
            showAlert();
            btn.setVisibility(View.GONE);
        }

Where method showTable()

private void showTable() {
        ArrayList<String> array_list = myDb.getAllContacts();

        ArrayAdapter arrayAdapter;
        arrayAdapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, array_list);

        //adding it to the list view.
        obj = (ListView) findViewById(R.id.listView1);
        obj.setAdapter(arrayAdapter);
    }

And method showAlert()

public void showAlert() {
        LayoutInflater inflater = (LayoutInflater) this.getSystemService(LAYOUT_INFLATER_SERVICE);
        View layout = inflater.inflate(R.layout.empty_basket, (ViewGroup) findViewById(R.id.root));
        AlertDialog.Builder adb = new AlertDialog.Builder(this);
        adb.setView(layout);
        adb.setCancelable(false);

        adb.setPositiveButton("Add items to basket", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                Intent i = new Intent(MyBasket.this, MainActivity.class);
                startActivity(i);
            }
        });
        adb.show();
    }

Any help will be appreciated.Thanks in advance.