我的目標是使用結構來包裝 sql.DB 來做一些比 sql.DB 更重要的事情。我創建的實例無法工作并在我運行時出現此錯誤。DbConn.db.prepare undefined (cannot refer to unexported field or method sql.(*DB)."".prepare)我的代碼是：type DatabaseConn struct {  driverName string  databaseName string  userName string  password string  dataSourceName string  db *sql.DB}func (d DatabaseConn)Open() error {    d.driverName    = DB_DRNAME    d.userName      = DB_UNAME    d.password      = DB_PWD    d.databaseName  = DB_DBNAME    d.dataSourceName = fmt.Sprintf("%s:%s@/%s?charset=utf8",d.userName, d.password, d.databaseName)    db, err := sql.Open(d.driverName, d.dataSourceName)    return err}func (d *DatabaseConn)Close() error {    defer func() {        if err := recover(); err != nil {            fmt.Println("Trying to handle error in DatabaseConn.Close(): ", err)        }    }()    err := d.db.Close()    return err}我正在嘗試創建一個實例并調用 sql.DB 方法。var dbConn DatabaseConndbConn.Open()defer dbConn.Close()dbQuery := fmt.Sprintf("SELECT *, FROM ms_node WHERE node_id = ?")getNodeRecord, err := dbConn.db.prepare(dbQuery)錯誤信息指向此處。./server.go:343: dbConn.db.prepare undefined (cannot refer to unexported field or method sql.(*DB)."".prepare)（個人背景：我是新手2周）