出现错误：SQLiteException: no such table: tabella (code1)

在访问数据库的时候， LogCat应用中出现错误：

SQLiteException: no such table: tabella (code1)

不知道原因在那儿啊，请帮忙。

SQLiteOpenHelper代码：

public class DatabaseHelper extends SQLiteOpenHelper {
    private static final String CREATE_DB_SQL = "CREATE TABLE tabella (_id INTEGER     PRIMARY KEY AUTOINCREMENT, colonna1 TEXT, colonna2 TEXT, colonna3 TEXT);";
    public DatabaseHelper(Context context) {
    super(context, "basedati", null, 1);
    }

    @Override
public void onCreate(SQLiteDatabase db) {

        db.execSQL(CREATE_DB_SQL);
        ContentValues cv = new ContentValues (3);
        cv.put("colonna1", "valore colonna 1");
        cv.put("colonna2", "valore colonna 3");
        cv.put("colonna3", "valore colonna 3");
        db.insert("tabella", "colonna1", cv);
}

@Override
    public void onUpgrade(SQLiteDatabase db, int arg1, int arg2) {
        db.execSQL("DROP TABLE IF EXISTS tabella");
        onCreate(db);   
    }
}

在activitiy中用来连接数据库的代码：

public class MainActivity extends Activity {
    private DatabaseHelper db=null;
    private Cursor constantsCursor=null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        db = new DatabaseHelper(this);

        constantsCursor=db.getReadableDatabase().rawQuery("SELECT colonna1 FROM  tabella ORDER BY colonna1", null);
        }
}

不能只改变Java的CREATE_DB_SQL，还要更新SQL:

public DatabaseHelper(Context context) {
    super(context, "basedati", null, 2); // Change the number to two 
}

非常感谢！有所收获！