【hive】with as語法

公用表表達式（CTE）是從WITH子句中指定的簡單查詢派生的臨時結果集（會把查詢的表數據放到內存中，供其他查詢隨時使用），該子句緊跟在SELECT或INSERT關鍵字之前。CTE僅在單個語句的執行範圍內定義。可以在Hive SELECT，INSERT， CREATE TABLE AS SELECT或CREATE VIEW AS SELECT語句中使用一個或多個CTE 。

在 select 中使用 CTE

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;

CTE in Views, CTAS, and Insert Statements

-- insert example
create table s1 like src;
with q1 as ( select key, value from src where key = '5')
from q1
insert overwrite table s1
select *;
 
-- ctas example
create table s2 as
with q1 as ( select key from src where key = '4')
select * from q1;
 
-- view example
create view v1 as
with q1 as ( select key from src where key = '5')
select * from q1;
select * from v1;
  
-- view example, name collision
create view v1 as
with q1 as ( select key from src where key = '5')
select * from q1;
with q1 as ( select key from src where key = '4')

參考：
[Hive進階]- Hive with as 語法
Hive中使用 with as 優化SQL