July 2023
Intermediate to advanced
278 pages
5h 40m
Chinese
Content preview from Trino 权威指南：原书第2版
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连接器
|
99
或者，你可以在空的目录中创建表，并期望数据在将来被
Trino
或外部源加载进来。无
论哪种情况，
Trino
都要求已经创建了目录结构；否则，执行
DDL
语句会出错。创建外
部表最常见的场景是与其他工具共享数据。
6.4.5
分区数据
到目前为止，你已经了解了一张表的数据，不管该表是内部的还是外部的，它都是以一
个或多个文件的形式存储在一个目录中。数据分区是这种方式的扩展，是一种将逻辑表
水平划分为更小块数据（称为分区）的技术。
这个概念本身源于
RDBMS
中的分区
schema
。
Hive
为
HDFS
中的数据引入了这种技术，
用于实现更好的查询性能并提升数据的可管理性。
如今，在分布式文件系统（如
HDFS
）和对象存储（如
S3
）中，分区已经成为标准的数
据组织策略。
下面用这个表的例子来说明分区：
CREATE TABLE datalake.web.page_views (
view_time timestamp,
user_id bigint,
page_url varchar,
view_date date
)
WITH (
partitioned_by = ARRAY['view_date']
)
在
partitioned_by
子句中列出的列必须是
DDL
中定义的最后一列。否
则，
Trino
会报错。
与非分区表一样，
page_views
表的数据在
.../page_views
目录中。使用分区可以改变表
布局的构建方式。对于分区表，在表目录中会添加其他的子目录。在下面的例子中，可
以看到由分区键定义的目录结构：
... ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.