Error UPDATE SQLite Request

It is required to update the rows of the table with the date corresponding to the condition. When calling a method for updating, an exception pops up.

android.database.sqlite.SQLiteException: near ".24": syntax error (code 1): , while compiling: UPDATE days_table SET expense = expense + 39.0 WHERE expdate = 2017.12.24 

What is the problem?

The code of the method in which the exception occurs

 @Override public void onClick(View v) { Intent intent = new Intent(); switch (v.getId()) { case R.id.etDate: DialogFragment dialogfragment = new DatePickerDialogClass(); dialogfragment.show(getFragmentManager(), "Date Picker Dialog"); break; case R.id.btnAdd: double dayExp; String day; String sCat ; String sComment; //Считывание данных из полей ввода dayExp = Double.parseDouble(etExp.getText().toString()); day = etDate.getText().toString(); sCat = tvSelCat.getText().toString(); sComment = etComm.getText().toString(); //Запись в БД boolean result = dbHelper.insertDayData(dayExp, sCat, day, sComment); if (result) { Toast.makeText(this, "Расход успешно добавлен", Toast.LENGTH_SHORT).show(); } else { Toast.makeText(this, "Ошибка! Расход не добавлен", Toast.LENGTH_SHORT).show(); } //Обновляем таблицу с днями dbHelper.updateDaysData(dayExp, day); setResult(RESULT_OK, intent); finish(); break; } } 

Method code for record update

  public void updateDaysData(double dayExp, String day) { SQLiteDatabase db = this.getWritableDatabase(); db.execSQL("UPDATE " + DAYS_TABLE_NAME + " SET " + DAYS_COL_2 + " = " + DAYS_COL_2 + " + " + dayExp + " WHERE " + DAYS_COL_4 + " = " + day); }