表1(A) 表2
a b c a c
1 2 1 4
3 4 3 5
我要把A中的c全部改为A中和B中a相同的c的值
update A
set A.c=B.c
from B where B.a=A.a
update A set c=(select c from B where A.a=B.a)
update A set c=B.c from B where A.a=B.a
update A set a.c = b.c from A join B on A.a = B.a