df1=pd.DataFrame({"date":[2015,2016,2017,2018,2019],"x1":[2000,3000,5000,8000,10000],"x2":[np.nan,"d"...on:指定连接使用的列(该列必须同时出现在两个DataFrame中),默认使用两个DataFrame中的所有同名列进行连接。...left_on / right_on:指定左右DataFrame中连接所使用的列。...df1=pd.DataFrame({"date":[2015,2016,2017,2018,2019],"x1":[2000,3000,5000,8000,10000],"x2":[np.nan,"d"...df1=pd.DataFrame({"date":[2015,2016,2017,2018,2019],"x1":[2000,3000,5000,8000,10000],"x2":[np.nan,"d"