I have two dataframes:
df1 (index is date):
a b
1900-01-01 1 2
1900-01-02 1 3
1900-01-03 3 3
df2(索引为整数):
c
0 3
1 1
合并后:
a b d
1900-01-01 1 2 3
1900-01-02 1 3 1
1900-01-03 3 3
我应该使用哪个函数?