spark学习（1）---dataframe操作大全

https://blog.csdn.net/dabokele/article/details/52802150

https://www.jianshu.com/p/009126dec52f

spark左外连接：https://blog.csdn.net/iduanyingjie/article/details/57449539

structField、structType、schame：https://blog.csdn.net/legotime/article/details/52643243

dataframe、dataset、sql.dataframe：https://www.cnblogs.com/seaspring/p/5831677.html