Hive语句的书写顺序及执行顺序

【hive调优】 hive建表设计层面调优 1.分区表 分区表,查询的时候只会扫描分区的数据,避免全表查询; 所以一定要用在查询时where条件中经常使用的字段作为分区字段,就比如datetime 2.分桶表 分桶表示hash散列,把一系列的记录按照hash散列进行分类; 一个分桶中会有多个不同的值,如果一个分桶中包含了某个值,那么这个值的所有的记录必然都在这个分桶中; 分桶经常使用的场景: join 采样 比如想去分析某个数据的中位数,或者平均值啊 最大最小值,从全表算是很消耗性能的;此时可以用分桶表,分桶表中的数据具备 阅读详情

1、Hive语句的书写顺序:(从前往后)
(1)select
(2)from
(3)join on
(4) where
(5)group by
(6)having
(7)distribute by/cluster by
(8) sort by
(9) order by
(10) limit
(11) union(去重不排序)/union all(不去重不排序)

 

2、Hive语句的执行顺序:
(1)from
(2)on
(3)join
(4)where
(5)group by
(6)having
(7)select
(8)distinct
(9)distribute by /cluster by
(10)sort by
(11) order by
(12) limit
(13) union /union all
 

 

保姆级教程:在Windows上用VS2019和OpenCV4.6搞定海康MV-EB435i RGBD相机图像采集 本文提供了一份详细的教程,指导如何在Windows环境下使用VS2019和OpenCV4.6配置海康MV-EB435i RGBD相机进行图像采集。从开发环境准备、SDK部署到代码移植和优化,涵盖了深度图与RGB图同步采集的实战技巧,帮助开发者快速上手工业级RGBD相机的应用开发。 阅读详情

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