来自 Javadoc :

为了获得最大的可移植性，应按从左到右的顺序读取每一行中的结果集列，并且每一列只能读取一次.

For maximum portability, result set columns within each row should be read in left-to-right order, and each column should be read only once.

在后台，您正在消耗TCP流中的字节，因此不能两次检索相同的列值也就不足为奇了.

Under the hood, you are consuming bytes from a TCP stream, so it isn't too surprising that you can't retrieve the same column value twice.