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 stylewith q1 as (select * from src where key= '5')from q1select *; -- chaining CTEswith 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 examplewith 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;