SQLITE Query between dates shows return value of 0.0 everytime

I am trying to query two dates start and finish and calculating the total in column price which is DOUBLE. My return value of sum always shows an output of 0.0 In the logcat I can see that the query is registered as Select Sum('price') From Cars where ('date_time') Between ('2017-03-09') AND ('2018-05-16'). Price is stored as double in database

//Budget Activity //Search Date Button

    mSearchdate = (Button) mRootView.findViewById(R.id.search_date);
    mSearchdate.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            String i = mdate1TextView.getText().toString();

            String b = mdate2TextView.getText().toString();

            double total =  db.getDateSum(i,b);
            mPriceTextView.setText(String.valueOf(total));


        }

    });

//Database helper class
// Getting total of price between 2 string dates

public double getDateSum(String start_date, String end_date){
    SQLiteDatabase db = this.getReadableDatabase();

    double sum= 0;
    //Toast.makeText(get, start_date + end_date, Toast.LENGTH_LONG).show();

Cursor cursor = db.rawQuery("SELECT SUM('" + Constants.COLUMN_PRICE + "') AS sum FROM '" + TABLE_CARS + "' WHERE date('" + Constants.COLUMN_DATETIME + "' ) BETWEEN date('" + start_date + "') AND date('" + end_date + "')", null);

    if(cursor.moveToFirst())
    {
        sum= cursor.getDouble(cursor.getColumnIndex("sum"));
        Log.i("TotalAmount :",sum+"");
        cursor.close();
    }

   return sum;

}