hive sql 列拆行、topn面试题简单总结

table1

id	city	view_count
1123	1,2,3	100
212123	2,3,4	110
212123	2,3	120

table2

city_id	city_name
1	北京
2	上海
3	广州
...	...

1. 写个sql把表1的id换成中文的list.

select collect_set(city_name), id
from
(
table2 join
select
id,city_id from table1 later view explode(city) **tmptable**  as city_id
on table2.city_id = tmptable.city_id
) innert
group by id

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2、取出来各个班级前三名平均分和姓名
row_number() over(order by xxx) 简单根据xxx排序
row_number() over(partition by xxxa order by xxxb) 按照xxxa分组，分组内按照xxxb排序

sum(amount) over(partition by name ordre by month)

---

ref:
explode语法：https://yq.aliyun.com/articles/654743

hive sql优化：https://cloud.tencent.com/developer/article/1423060

练习题：
https://www.jianshu.com/p/faee67f104f7
https://blog.csdn.net/qq_43081842/article/details/102832142

算法人必懂的Hive知识-四道Hive面试&笔试题解析