求一sql

[Dabay]

Food表中我加了一列Counter,这一列的值应该是在另外一个表中UserFood中Food.ID出现的次数,请问这个sql如何写.
我用这个select [ID],IsNULL((Select count(1) from UserFood where UserFood.FoodID = Food.ID),0) from Food,可以等到想要的值,但是不知道如何插入到Food表中.谢谢!!!

Food表
-------------
ID FoodName Counter
-------------
1 第一个 NULL
2 第二个 NULL
3 第三个 NULL


UserFood表
-------------
ID FoodID
-------------
1 1
2 2
3 1
4 1

想要的结果是:
Food表
-------------
ID FoodName Counter
-------------
1 第一个 3
2 第二个 1
3 第三个 0

[谢良]

update Food表
set Counter =
isnull((select count(FoodID) from UserFood where FoodID = Food.ID),0)
from Food

[hellowork]

update a set Counter =
isnull((select count(1) from UserFood where FoodID = a.ID),0)
from Food a