Hive 窗口函数详细介绍3 lag，lead，first_value，last_value

这篇文章继续介绍4个窗口函数。

lag

lag(column_name,n,default):用于统计窗口内往上第n行的值，第一个参数为列名，第二个参数为往上第n行（可选，默认为1），第三个参数为默认值（当往上n行为null时，取默认值，若不指定，则为null）

lead

lead与lag想法，lead（column_name，n，default）用于统计窗口内向下取n行的值

first_value

first_value()  取分组排序后，截止到当前行的第一个值

last_value

last_value() 取分组排序后，截止到当前行的最后一个值

 

下面通过具体的实例介绍它们的用法

create  table  if   not    exists   buy_info  (
    
 name   string,
 buy_date   string,
 buy_num   int
)
row  format  delimited  fields   terminated  by  '|';


select  *  from   buy_info;

name	buy_date	buy_num
zhangsan	2020-02-23	21
zhangsan	2020-03-12	34
zhangsan	2020-04-15	12
zhangsan	2020-05-12	51
lisi	2020-03-16	12
lisi	2020-03-21	24
lisi	2020-07-12	41
lisi	2020-07-27	32

 

 

 

 

 

 

 

 

 

 

 

select   name , buy_date,buy_num，
lag(buy_date,1,'1970-01-01')  over(partition  by  name  order  by  buy_date)   as last_date, lead(buy_date,1,'2020-12-31') over(partition by name order by buy_date) as next_date, first_value () over(partition by name order by buy_date) as first_date, last_value() over(partition by name order by buy_date) as last_date from buy_info; 

 

查询结果如下

name	buy_date	buy_num	last_date	next_date	first_date	last_date
zhangsan	2020-02-23	21	1970-01-01	2020-03-12	2020-02-23	2020-05-12
zhangsan	2020-03-12	34	2020-02-23	2020-04-15	2020-02-23	2020-05-12
zhangsan	2020-04-15	12	2020-03-12	2020-05-12	2020-02-23	2020-05-12
zhangsan	2020-05-12	51	2020-04-15	2020-12-31	2020-02-23	2020-05-12
lisi	2020-03-16	12	1970-01-01	2020-03-21	2020-03-16	2020-07-27
lisi	2020-03-21	24	2020-03-16	2020-07-12	2020-03-16	2020-07-27
lisi	2020-07-12	41	2020-03-21	2020-07-27	2020-03-16	2020-07-27
lisi	2020-07-27	32	2020-07-12	2020-12-31	2020-03-16	2020-07-27