Hive - 优化自我加入

Question

我们说我有以下问题：

select a.model, a.engine_size, b.engine_size from (

  select model, engine_size
  from cars
  where number_of_doors = 4
) a

inner join (

  select model, engine_size
  from cars
  where number_of_doors = 4
) b

on (a.model = b.model);

我在这里重复一个子查询。我只是想知道以下内容是否更加优化＆＃39;或者是否会自动缓存重复的子查询结果？

with features as (

  select model, engine_size
  from cars
  where number_of_doors = 4
)

select a.model, a.engine_size, b.engine_size
from features a
inner join features b
on (a.model = b.model);

这些中的任何一个会更有效吗？

谢谢！

Answer 1

一种方法是通过自我加入，但场景没有任何意义

select a.model, a.engine_size,b.engine_size
from   cars a 
join   cars b 
on     (a.model = b.model)
where  a.number_of_doors = 4