Spark SQL广播提示中间表 [英] Spark SQL broadcast hint intermediate tables

问题描述

我在使用广播提示时遇到了问题(也许是缺乏SQL知识).

I have a problem using Broadcast hints (maybe is some lack of SQL knowledge).

我有一个类似的查询

SELECT * /* broadcast(a) */
FROM a 
INNER JOIN b
ON ....
INNER JOIN c
on ....

我想做

SELECT * /* broadcast(a) */
FROM a 
INNER JOIN b 
ON ....
INNER JOIN c /* broadcast(AjoinedwithB) */
on ....

我的意思是，我想强制广播连接(我宁愿避免更改spark参数以将其强制到任何地方)，但是我不知道如何引用名为AjoinedwithB

I mean, I want to force broadcast join (I would prefer to avoid changing spark parameters to force it everywhere), but I don't know how to refer to the table named AjoinedwithB

我当然可以拆分SQL，使用DF API等.但是我想在一个SQL查询中完成.

Of course I can split the SQL, work with DF API and such... but I would like to do it in a single SQL Query.

推荐答案

您可以使用任一子查询

SELECT /*+ broadcast(a_b) */ *
FROM 
    (SELECT /*+ broadcast(a) */ * FROM a JOIN b ON ...) AS a_b 
    JOIN c ON ...

或CTE:

WITH a_b AS (SELECT /*+ broadcast(a) */ * FROM a JOIN b ON ...)
SELECT /*+ broadcast(a_b) */ * FROM a_b JOIN c ON ...

这篇关于Spark SQL广播提示中间表的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！