why fdisk -l /dev/block/mmcblk0 replays "no partition table?"

[youxiaojie]

I rooted nexus 9, disable force encryption , adb shell, su, fdisk -l /dev/block/mmcblk0 why the phone replays "no partition table?"
the same then boot into twrp fdisk -l /dev/block/mmcblk0
command returned "no valid partition table"?
and where /dev/block/mmcblk0p* comes from?