Spark sql -- Spark sql中的窗口函数和对应的api

一、窗口函数种类

1. ranking 排名类
2. analytic 分析类
3. aggregate 聚合类

Function Type	SQL	DataFrame API	Description
Ranking	rank	rank	rank值可能是不连续的
Ranking	dense_rank	denseRank	rank值一定是连续的
Ranking	percent_rank	percentRank	相同的分组中 (rank -1) / ( count(score) - 1 )
Ranking	ntile	ntile	将同一组数据循环的往n个桶中放，返回对应的桶的index，index从1开始
Ranking	row_number	rowNumber	很单纯的行号，类似excel的行号
Analytic	cume_dist	cumeDist
Analytic	first_value	firstValue	相同的分组中最小值
Analytic	last_value	lastValue	相同的分组中最大值
Analytic	lag	lag	取前n行数据
Analytic	lead	lead	取后n行数据
Aggregate	min	min	最小值
Aggregate	max	max	最大值
Aggregate	sum	sum	求和
Aggregate	avg	avg	求平均

二、具体用法如下

count(...) over(partition by ... order by ...)--求分组后的总数。
sum(...) over(partition by ... order by ...)--求分组后的和。
max(...) over(partition by ... order by ...)--求分组后的最大值。
min(...) over(partition by ... order by ...)--求分组后的最小值。
avg(...) over(partition by ... order by ...)--求分组后的平均值。
rank() over(partition by ... order by ...)--rank值可能是不连续的。
dense_rank() over(partition by ... order by ...)--rank值是连续的。
first_value(...) over(partition by ... order by ...)--求分组内的第一个值。
last_value(...) over(partition by ... order by ...)--求分组内的最后一个值。
lag() over(partition by ... order by ...)--取出前n行数据。　　
lead() over(partition by ... order by ...)--取出后n行数据。
ratio_to_report() over(partition by ... order by ...)--Ratio_to_report() 括号中就是分子，over() 括号中就是分母。
percent_rank() over(partition by ... order by ...)--

三、实际例子

案例数据：/root/score.json/score.json，学生名字、课程、分数

{"name":"A","lesson":"Math","score":100}
{"name":"B","lesson":"Math","score":100}
{"name":"C","lesson":"Math","score":99}
{"name":"D","lesson":"Math","score":98}
{"name":"A","lesson":"E","score":100}
{"name":"B","lesson":"E","score":99}
{"name":"C","lesson":"E","score":99}
{"name":"D","lesson":"E","score":98}

select
name,lesson,score,
ntile(2) over (partition by lesson order by score desc ) as ntile_2,
ntile(3) over (partition by lesson order by score desc ) as ntile_3,
row_number() over (partition by lesson order by score desc ) as row_number,
rank() over (partition by lesson order by score desc ) as rank,
dense_rank() over (partition by lesson order by score desc ) as dense_rank, 
percent_rank() over (partition by lesson order by score desc ) as percent_rank 
from score 
order by lesson,name,score

输出结果完全一样，如下表所示

name	lesson	score	ntile_2	ntile_3	row_number	rank	dense_rank	percent_rank
A	E	100	1	1	1	1	1	0.0
B	E	99	1	1	2	2	2	0.3333333333333333
C	E	99	2	2	3	2	2	0.3333333333333333
D	E	98	2	3	4	4	3	1.0
A	Math	100	1	1	1	1	1	0.0
B	Math	100	1	1	2	1	1	0.0
C	Math	99	2	2	3	3	2	0.6666666666666666
D	Math	98	2	3	4	4	3	1.0

参考：

spark sql中的窗口函数

over(partition by) 函数

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原创文章，转载请务必将下面这段话置于文章开头处（保留超链接）。
本文转发自程序媛说事儿，原文链接https://www.cnblogs.com/abc8023/p/10910741.html

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