sql - Hive - 优化自连接

Question

假设我有以下查询:

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。我只是想知道以下是否更“最优”，或者重复子查询的结果是否会自动缓存？

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);

这两者中的任何一个都会更有效率吗？

Answer 1

一种方法是进行自连接，但这种情况没有任何意义

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