1、Hive查询报错 Invalid table alias or column reference 'create_time': (possible column names are: _c0, _c1

解决办法：https://blog.csdn.net/qq_31573519/article/details/52790671

2、hive日期格式转换  

将 Tue May 20 22:41:01 CST 2014 转换为： yyyy-MM-dd HH:mm:ss

http://www.360doc.com/content/18/0626/21/8772388_765637973.shtml

3、group by去重

SELECT user_name,commentid,collect_set(title)[0] as title,collect_set(source)[0] as source,collect_set(content)[0] as content ,collect_set(time)[0] as time,collect_set(car_model)[0] as car_model FROM user_2morecars GROUP BY user_name,commentid；————————————————版权声明：本文为CSDN博主「HFUT_qianyang」的原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接及本声明。原文链接：https://blog.csdn.net/qy20115549/article/details/83831307

4、hive分区表添加字段出现新增字段null的bug

原因：hive里面的类型是string

oracle里面有varchar(2)he number

处理方法：

oracle里面number类型的在hive上进行处理：