hive中的with用法

hive 可以通过with查询来提高查询性能，因为先通过with语法将数据查询到内存，然后后面其它查询可以直接使用，这种方法与创建临时表类似但是不需要创建临时表实体表，内存中的子查询结果在会话结束后会自动删除。

with q1 as ( select key from src where key = '5')

select *

from q1;

 

-- from style

with q1 as (select * from src where key= '5')

from q1

select *;

 

-- chaining CTEs

with q1 as ( select key from q2 where key = '5'),

q2 as ( select key from src where key = '5')

select * from (select key from q1) a;

 

-- union example

with q1 as (select * from src where key= '5'),

q2 as (select * from src s2 where key = '4')

select * from q1 union all select * from q2;