There is a FAQ on Sony's website. Please see the link as below.
http://www.sony.com.au/support/faq/474653/product/sgpt122au
Unfortunately, it didn't resolve the issue. I followed the steps in FAQ many times, while system (Windows 7) still couldn't find the driver.
When checked the device properties, I found the following page which showing the Hardware Ids.
Then I did the search with those Ids, found the descriptions as below. And append those descriptions into android_winusb.inf file, then tried to update the driver again. It worked!
;SONY Sony Tablet P
%SingleAdbInterface% = USB_Install, USB\VID_054C&PID_04D2
%CompositeAdbInterface% = USB_Install, USB\VID_054C&PID_04D2&MI_01
;SONY Sony Tablet S
%SingleAdbInterface% = USB_Install, USB\VID_054C&PID_05B4
%CompositeAdbInterface% = USB_Install, USB\VID_054C&PID_05B4&MI_01
;SONY Xperia Tablet S
%SingleAdbInterface% = USB_Install, USB\VID_054C&PID_06AD
%CompositeAdbInterface% = USB_Install, USB\VID_054C&PID_06AD&MI_01
;SONY Walkman Z
%SingleAdbInterface% = USB_Install, USB\VID_054C&PID_0691
%CompositeAdbInterface% = USB_Install, USB\VID_054C&PID_0691&MI_01
Hope this can help people save some time.