Hive中window as与with as的用法

Hive中window as与with as的用法 Hive中自定义变量的用法

承接上篇Hive窗口帧文章，具体主页有

两个窗口帧方式：rows、range

range格式：如果当前值在80，求前2后2所有值的平均值， 取值就会在80-2=78和80+2=82之内的所有行

//格式1
avg(score) over (partition by clazz order by score desc range between 2 perceding and 2 following)

select *,
row_number() over(partition by clazz order by score desc) as num,
rank() over(partition by clazz order by score desc) as num2,
avg(score) over(partition by clazz order by score desc rows between 1 preceding and 1 following) as avg1,
max(score) over(partition by clazz order by score desc rows between 2 preceding
and current row) as max1,
avg(score) over (partition by clazz order by score desc range between 2 preceding and 2 following) as avg2
from testwins;

优化sql语句

WINDOW w AS (partition by clazz order by score desc)
等同于
window w = (partition by clazz order by score desc)
变量值类型 变量名 = 赋值

select *,
row_number() over w as num,
rank() over w as num2,
avg(score) over(partition by clazz order by score desc rows between 1 preceding and 1 following) as avg1,
max(score) over(partition by clazz order by score desc rows between 2 preceding
and current row) as max1,
avg(score) over (partition by clazz order by score desc range between 2 preceding and 2 following) as avg2
from testwins
WINDOW w AS (partition by clazz order by score desc);

联表联查中用的最多

create table students(
id bigint,
name string,
age int,
gender string,
clazz string
)
ROW FORMAT DELIMITED FIELDS TERMINATED BY ',';

create table score(
id bigint,
course_id string,
score int
)
ROW FORMAT DELIMITED FIELDS TERMINATED BY ',';

在学生表后面显示成绩

//MySQL简单版本
select students.*,score.score from students left join score on students.id=score.id;

//MySQL复杂版本
select * from (select id,sum(score) as score from (select students.*,score.score from students left join score on students.id=score.id) as stu group by id) as s1
left join (select students.*,score.score from students left join score on students.id=score.id) as s2
on s1.id=s2.id;

with as使用
例子:
  //hive版本的
  with stu as (select students.*,score.score from students left join score on students.id=score.id)
  with s1 as ((select id,sum(score) as score from stu group by id))
  //使用with as 
  select * from s1
  left join stu 
  on s1.id=stu.id;