序列函数

1.ROW_NUMBER()

row_number() OVER (PARTITION BY COL1 ORDER BY COL2)

表示根据COL1分组，在分组内部根据 COL2排序，而此函数计算的值就表示每组内部排序后的顺序编号（组内连续的唯一的)。

-- rn_id 按照性别分组，按照id排序
select sex,name,id,
row_number() over(partition by sex order by id desc) as rn_id
from student_grouping;

-- 运行结果
MapReduce Jobs Launched:
Stage-Stage-1: Map: 1 Reduce: 1 Cumulative CPU: 3.07 sec HDFS Read: 9758 HDFS Write: 298 SUCCESS
Total MapReduce CPU Time Spent: 3 seconds 70 msec
OK

boy     name6   6       1
boy     name5   5       2
boy     name4   4       3
boy     name2   2       4
boy     name1   1       5
girl    name8   8       1
girl    name7   7       2
girl    name3   3       3

一个查询语句，有两个row_number()，并且两个分组一样，但排序不一样，查询出来的数据会跟着哪个走？

-- rn_id 按照性别分组，按照id排序
-- rn_age 按照性别分组，按照age 排序
select sex,name,id,age,
row_number() over(partition by sex order by id desc) as rn_id,
row_number() over(partition by sex  order by age desc) as rn_age
from student_grouping;

查询结果：

2.RANK()、dense_rank()

select sex,name,id,age,
rank() over(partition by sex order by age desc) as rk1,
dense_rank() over(partition by sex  order by age desc) as rk2,
row_number() over(partition by sex order by age desc) as rn1
from student_grouping;

查询结果