Impala GROUP BY分区列 [英] Impala GROUP BY partitioned column

问题描述

理论问题

让我们说我的表有四列:A，B，C，D. A和D的值相等，表按A列划分.

Lets say I have table with four columns : A,B,C,D. Values of A and D are equal, table is partitioned by column A.

明智的性能，如果我发出此查询，会有所不同吗? 按A选择SUM(B)GROUP; 或这一个: SELECT SUM(B)GROUP BY D;

Performance wise, would it make any difference if I issue this query SELECT SUM(B) GROUP BY A ; or this one : SELECT SUM(B) GROUP BY D ;

我要问的是，通过在分区列上使用GROUP BY可以提高性能吗?

In different words I'm asking, is there any performance gain by using the GROUP BY on partitioned column ?

谢谢

推荐答案

如果在过滤器(SQL中的WHERE子句)中使用分区列，通常可以提高性能

Usually there are performance gains if you use the partitioned columns on a filter (WHERE clause in your SQL)

由于两个查询都使用全表扫描"，因此两个查询之间应该没有太大差异.如果存在很多分区(例如大约50K)，您可能会发现差异，这往往会降低查询性能，但通常情况并非如此.

since both queries use a "full table scan" it should not have a lot of difference between both queries. You might see a difference if theres is a lot of partitions (Like around 50K), with tends to degrade the query performance, but that is not usually the case.

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