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Reference

• Hive
• Oracle
• MySQL

概述

• 代码准备(hive)

-- ALTER TABLE order RENAME TO order_infoscreate table order_infos(name varchar(20), order_date date, cost int)insert into order_infosselect 'jack',cast('2015-01-01' as date),10union all                select 'tony',cast('2015-01-02' as date),15union all                select 'jack',cast('2015-02-03' as date),23union all                select 'tony',cast('2015-01-04' as date),29union all                select 'jack',cast('2015-01-05' as date),46union all                select 'jack',cast('2015-04-06' as date),42union all                select 'tony',cast('2015-01-07' as date),50union all                select 'jack',cast('2015-01-08' as date),55union all                select 'mart',cast('2015-04-08' as date),62union all                select 'mart',cast('2015-04-09' as date),68union all                select 'neil',cast('2015-05-10' as date),12union all                select 'mart',cast('2015-04-11' as date),75union all                select 'neil',cast('2015-06-12' as date),80union all                select 'mart',cast('2015-04-13' as date),94

• 当同一个select查询中存在多个窗口函数时,他们相互之间是没有影响的.每个窗口函数应用自己的规则.
• window子句
  • PRECEDING：往前
  • FOLLOWING：往后
  • CURRENT ROW：当前行
  • UNBOUNDED：起点
    • UNBOUNDED PRECEDING：从前面的起点
    • UNBOUNDED FOLLOWING：到后面的终点
• 如果只使用partition by子句，未指定order by的话,我们的聚合是分组内的聚合
• 使用了order by子句，未使用window子句的情况下,默认从起点到当前行

select name,order_date,cost,sum(cost) over() as sample1, --在每一行后面增加 所有行相加sum(cost) over(partition by name) as sample2,--在每一行后面增加 按name分组，组内数据 相加sum(cost) over(partition by name order by order_date) as sample3,--在每一行后面增加 按name分组，组内数据 累加sum(cost) over(partition by name order by order_date rows between UNBOUNDED PRECEDING and current row )  as sample4 ,--和sample3一样,由起点到当前行的聚合sum(cost) over(partition by name order by order_date rows between 1 PRECEDING   and current row) as sample5, --当前行和前面一行做聚合sum(cost) over(partition by name order by order_date rows between 1 PRECEDING   AND 1 FOLLOWING  ) as sample6,--当前行和前边一行及后面一行sum(cost) over(partition by name order by order_date rows between current row and UNBOUNDED FOLLOWING ) as sample7 --当前行及后面所有行from testtest.order_infos;

• 排序
  • row_number()：从1开始，按照顺序，生成分组内记录的序列,row_number()的值不会存在重复,当排序的值相同时,按照表中记录的顺序进行排列
  • RANK()： 生成数据项在分组中的排名，排名相等会在名次中留下空位 （排序相同时不连续）。RANK() OVER(PARTITION BY cookieid ORDER BY pv desc) AS rn
  • DENSE_RANK()： 生成数据项在分组中的排名，排名相等会在名次中不会留下空位（排序连续）
• LAG(向上，向前)和LEAD(向下，向后)函数：可以返回上下数据行的数据

select name,order_date,cost,lag(order_date,1,'1900-01-01') over(partition by name order by order_date ) as time1, -- 购买时间lag(order_date,2) over (partition by name order by order_date) as time2 -- 购买时间对应的上一次的购买时间from testtest.order_infos

• first_value取分组内排序后，截止到当前行，第一个值
• last_value取分组内排序后，截止到当前行，最后一个值

select name,order_date,cost,first_value(order_date) over(partition by name order by order_date) as time1,last_value(order_date) over(partition by name order by order_date) as time2from testtest.order_infos

• MySQL
  • 说明：MySQL从8.0开始支持窗口函数
  • 常见窗口函数
    • row_number()
    • rank()
    • dense_rank()
    • percent_rank()：当前记录排序的(rank() - 1) 除以 (分组总记录数 - 1)的百分比
    • cume_dist()：计算当前记录排序rank()的总记录数除以分组总记录数的百分比
    • lag(col,N)：按照分组排序，显示该记录的前N个的col值
    • lead(col,N)
    • first_value(col)：按照分组排序，显示排序第一的col值
    • last_value(col)
    • nth_value(col,N)：按照分组排序，截止到当前记录第N排序的col值
    • nfile(N)：按照分组排序，将所有记录分为N份

-- row_number()-- 8.0select row_number() over w as row_num,class_num,user_id,score from score where subject_name='Math' window  w as ( partition by class_num order by score desc) ;-- 8.0之前select `row_number`,class_num,user_id,score from (select if(@class=class_num,@r:=@r+1,@r:=1) as `row_number`,@class:=class_num,class_num,user_id,score from score,(select @r:=0,@class=NULL) temp order by class_num,score desc) tmp2;-- dense_rank()-- 8.0select dense_rank() over w as `dense_rank`,class_num,user_id,score from score where subject_name='Math' window  w as ( partition by class_num order by score desc) ;-- 8.0之前select `dense_rank`,class_num,user_id,score from (select if(@class=class_num,case when  @s = score then @r when @s := score then @r := @r + 1 end,@r:=1) as `dense_rank`,@class:=class_num,@s:=score,class_num,user_id,score FROM score, ( SELECT @r := 0, @s = NULL,@class=NULL ) temp where subject_name = 'Math' order by  class_num,score desc) temp2;-- rank()-- 8.0select rank() over w as `rank`,class_num,user_id,score from score where subject_name='Math' window  w as ( order by score desc) ;-- 8.0之前select `rank`,class_num,user_id,score from (SELECT  @r:=if(@s = score,@r,@c)  AS `rank`,@s:=score,@c:=@c+1,class_num,user_id,score from score, ( select @r := 0, @s = NULL,@c:=1 ) r where subject_name = 'Math' order by score desc) temp;

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