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怎么建设分销模式手机网站,仙桃网站制作,新沂做网站,优化师培训hive开窗函数 文章目录hive开窗函数1. 开窗函数概述1.1 窗口函数分类1.2 窗口函数和普通聚合函数的区别2. 窗口函数的基本用法2.1 基本用法2.2 设置窗口的方法2.2.1 window_name2.2.2 partition by2.2.3 order by 子句2.2.4 rows指定窗口大小窗口框架2.3 开窗函数中加 order by…hive开窗函数 文章目录hive开窗函数1. 开窗函数概述1.1 窗口函数分类1.2 窗口函数和普通聚合函数的区别2. 窗口函数的基本用法2.1 基本用法2.2 设置窗口的方法2.2.1 window_name2.2.2 partition by2.2.3 order by 子句2.2.4 rows指定窗口大小窗口框架2.3 开窗函数中加 order by 和不加 order by 的区别3. 窗口函数用法举例3.1 序号函数 row_number() / rank() / dese_rank()3.2 分布函数: percent_rank() / cume_dist()3.2.1 percent_rank()3.2.2 cume_dist()3.2.3 前后函数lag(expr, n, defval) 、 lead(expr, n, defval)3.2.4 头尾函数first_value(expr) 、 last_value(expr)4 聚合函数窗口函数1. 开窗函数概述 窗口函数也称OLAP函数对数据库进行实时分析处理 1.1 窗口函数分类 序号函数row_number() / rank() / dense_rank()分布函数percent_rank() / cume_dist()前后函数lag() / lead()头尾函数first_val() / last_val()聚合函数窗口函数sum() over()、 max()/min() over() 、avg() over()其他函数nth_value() / nfile() 1.2 窗口函数和普通聚合函数的区别 聚合函数是将多条记录聚合成一条窗口函数是每条记录都会执行有几条记录执行完还是几条 窗口函数兼具group by子句的分组功能和order by子句的排序功能但是partition by 子句不具备group by的汇总功能

1. 窗口函数的基本用法 准备基础数据 CREATE TABLE exam_record (uid int COMMENT 用户ID,exam_id int COMMENT 试卷ID,start_time timestamp COMMENT 开始时间,submit_time timestamp COMMENT 提交时间,score tinyint COMMENT 得分 ) COMMENT 考试记录表 ROW FORMAT DELIMITED FIELDS TERMINATED BY , STORED AS TEXTFILE TBLPROPERTIES (skip.header.line.count1);INSERT INTO exam_record(uid,exam_id,start_time,submit_time,score) VALUES (1006, 9003, 2021-09-07 10:01:01, 2021-09-07 10:21:02, 84), (1006, 9001, 2021-09-01 12:11:01, 2021-09-01 12:31:01, 89), (1006, 9002, 2021-09-06 10:01:01, 2021-09-06 10:21:01, 81), (1005, 9002, 2021-09-05 10:01:01, 2021-09-05 10:21:01, 81), (1005, 9001, 2021-09-05 10:31:01, 2021-09-05 10:51:01, 81), (1004, 9002, 2021-09-05 10:01:01, 2021-09-05 10:21:01, 71), (1004, 9001, 2021-09-05 10:31:01, 2021-09-05 10:51:01, 91), (1004, 9002, 2021-09-05 10:01:01, 2021-09-05 10:21:01, 80), (1004, 9001, 2021-09-05 10:31:01, 2021-09-05 10:51:01, 80);select * from exam_record;exam_record.uid exam_record.exam_id exam_record.start_time exam_record.submit_time exam_record.score 1006 9001 2021-09-01 12:11:01 2021-09-01 12:31:01 89 1006 9002 2021-09-06 10:01:01 2021-09-06 10:21:01 81 1005 9002 2021-09-05 10:01:01 2021-09-05 10:21:01 81 1005 9001 2021-09-05 10:31:01 2021-09-05 10:51:01 81 1004 9002 2021-09-05 10:01:01 2021-09-05 10:21:01 71 1004 9001 2021-09-05 10:31:01 2021-09-05 10:51:01 91 1004 9002 2021-09-05 10:01:01 2021-09-05 10:21:01 80 1004 9001 2021-09-05 10:31:01 2021-09-05 10:51:01 802.1 基本用法 窗口函数语法 窗口函数 over[(partition by 列表清单)] order by 排序列表清单 [rows between 开始位置 and 结束位置]窗口函数指要使用的分析函数 over(): 用来指定窗口函数的范围如果括号中什么都不写则窗口包含where的所有行 select uidscore,sum(score) over() as sum_score from exam_record;运行结果 uid score sum_score 1006 89 654 1006 81 654 1005 81 654 1005 81 654 1004 71 654 1004 91 654 1004 80 654 1004 80 6542.2 设置窗口的方法 2.2.1 window_name 给窗口指定一个别名 select uid,score,rank() over my_window_name as rk_num,row_number() over my_window_name as row_num from exam_record window my_window_name as (partition by uid order by score);2.2.2 partition by select uid,score,sum(score) over(partition by uid) as sum_score from exam_record;按照uid进行分组分别求和 使用row_number()序号函数表明序号 selectuid,score,row_number() over(partition by uid) as row_num from exam_record;2.2.3 order by 子句 按照哪些字段进行排序窗口函数将按照排序后的记录进行编号 selectuid,score,row_number() over (partition by uid order by score desc) as row_num from exam_record单独使用order by uid selectuid,score,sum(score) over (order by uid desc) as row_num from exam_record;单独使用partition by uid selectuid,score,sum(score) over (partition by uid) as row_num from exam_record;partition by进行分组内的求和分区间独立 order by 对序号相同的进行求和对序号不同的进行累加求和 单独使用order by score selectuid,score,sum(score) over (order by score desc) as row_num from exam_record;2.2.4 rows指定窗口大小 查看score的平均值 selectuid,score,avg(score) over(order by score desc) as avg_num from exam_record按照score降序排列每一行计算前一行到当前行的score的平均值 selectuid,score,avg(score) over(order by row_score) as avg_num from(selectuid,score,row_number() over(order by score desc) as row_scorefrom exam_record)res窗口框架 指定窗口大小框架是对窗口的进一步分区框架有两种限定方式 使用rows语句通过指定当前行之前或之后的固定数目的行来限制分区中的行数 使用range语句按照排列序列的当前值根据相同值来确定分区中的行数 order by 字段名 range|rows 边界规则0 | [between 边界规则1] and 边界规则2 range和rows的区别 range按照值的范围进行范围的定义rows按照行的范围进行范围的定义 使用框架时必须要有order by子句如果仅指定了order by子句未指定框架则默认框架会使用range unbounded preceding and current row 从第一行到当前行的数据如果窗口函数没有指定order by子句就不存在 rows|range 窗口的计算range 只支持使用unbounded 和 current row 查询我与前两名的平均值 selectuid,score,avg(score) over(order by score desc rows 2 preceding) as avg_score from exam_record;查询当前行及前后一行的平均值 selectuid,score,avg(score) over(order by score desc rows between 1 preceding and 1 following) as avg_score from exam_record;2.3 开窗函数中加 order by 和不加 order by 的区别 当开窗函数为排序函数时如row_number()、rank()等over中的order by 只起到窗口内排序的作用 当开窗函数为聚合函数时如max、min、count等over中的order by不仅对窗口内排序还起到窗口内从当前行到之前所有行的聚合 selectuid,exam_id,start_time,sum(score) over(partition by uid) as one,sum(score) over(partition by uid order by start_time) as two from exam_record3. 窗口函数用法举例 3.1 序号函数 row_number() / rank() / dese_rank() 区别rank() : 并列排序跳过重复序号——1、1、3 ​ row_number() : 顺序排序——1、2、3 ​ dese_rank() : 并列排序不跳过重复序号——1、1、2 selectuid,score,rank() over my_window as rk_num,row_number() over my_window as row_num from exam_record window my_window as (partition by uid order by score);不使用窗口函数实现分数排序 SELECTP1.uid,P1.score,(SELECTCOUNT(P2.score)FROM exam_record P2WHERE P2.score P1.score) 1 AS rank_1 FROM exam_record P1 ORDER BY rank_1;3.2 分布函数: percent_rank() / cume_dist() 3.2.1 percent_rank() percent_rank() 函数将某个数据在数据集的排位作为数据集的百分比值返回范围0到1 按照(rank - 1) / (rows - 1)进行计算rank为rank()函数产生的序号rows为当前窗口的记录总行数 selectuid,score,rank() over my_window as rank_num,percent_rank() over my_window as prk from exam_record window my_window as (order by score desc)3.2.2 cume_dist() 如果升序排列则统计小于等于当前值的行数 / 总行数 如果降序排列则统计大于等于当前值的行数 / 总行数 查询小于等于当前score的比例 selectuid,score,rank() over my_window as rank_num,cume_dist() over my_window as cume from exam_record window my_window as (order by score asc);3.2.3 前后函数lag(expr, n, defval) 、 lead(expr, n, defval) lag()和lead()函数可以在同一次查询中取出同一字段前 n 行的数据和后 n 行的数据作为独立列 lag( exp_str,offset,defval) over(partition by .. order by …)lead(exp_str,offset,defval) over(partition by .. order by …)exp_str 是字段名offset是偏移量即 n 的值defval默认值如何当前行向前或向后 n 的位置超出表的范围则会将defval的值作为返回值默认为NULL 查询前1名同学和后一名同学的成绩和当前同学成绩的差值 先将前一名、后一名以及当前行的分数放在一起 selectuid,score,lag(score, 1, 0) over my_window as before,lead(score, 1, 0) over my_window as next from exam_record window my_window as (order by score desc);然后做差值 selectuid,score,score - before as before,score - next as next from (selectuid,score,lag(score, 1, 0) over my_window as before,lead(score, 1, 0) over my_window as next from exam_record window my_window as (order by score desc))res3.2.4 头尾函数first_value(expr) 、 last_value(expr) 返回第一个exprfirst_value(expr)返回第二个exprlast_value(expr) 查询第一个和最后一个分数 selectuid,score,first_value(score) over my_window as first,last_value(score) over my_window as last from exam_record window my_window as (order by score desc);4 聚合函数窗口函数 窗口函数在where之后执行所以where需要用窗口函数作为条件 SELECTuid,score,sum(score) OVER my_window_name AS sum_score,max(score) OVER my_window_name AS max_score,min(score) OVER my_window_name AS min_score,avg(score) OVER my_window_name AS avg_scoreFROM exam_recordWINDOW my_window_name AS (ORDER BY score desc)