What shall I wear to keep me warm since I will be going to Shanghai in mid dec?

If there is no cold air, the average temperature is around 5 to 10C and it is suggested to wear the thick coat and thick sweaters.
In my opinion, it is suggested to take a down jacket in case of the sudden cold air.

Thank you for your answer, however, regarding the thickness of the coat, how thick is consider thick? I have just bought a coat/wind breaker but some of my friend who never been there says its not thick enough to keep me warm. I am rather confused. Another thing, what type of hand gloves/cream/medication do I need to bring along? Thank you.

wind breaker plus a sweater can be fine. Don't worry!

The most ordinary gloves can be ok!

I knew most people from tropical countries could not stand the cold in Shanghai mid Dec. I think it is better for you to wear long john as well as wearing down jacket.