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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高级连接器示例
|
115
表时，必须使用
column_mapping
表属性。你必须在创建表时将
external
属性设置为
true
：
CREATE TABLE accumulo.ontime.flights (
rowid VARCHAR,
flightdate VARCHAR,
flightnum, INTEGER,
origin VARCHAR
dest VARCHAR
)
WITH
external = true,
column_mapping = 'origin:location:origin,dest:location:dest'
);
7.2.2 Accumulo
中的谓词下推
在
Accumulo
连接器中，
Trino
可以利用
Accumulo
内置的二级索引。为此，
Accumulo
连接器需要在每个
tablet
服务器上建立一个自定义的服务器端迭代器。该迭代器以
JAR
文件的形式分发，你必须将其复制到每个
tablet
服务器上的
$ACCUMULO_HOME/lib/ext
目录中。你可以在
Trino
文档中找到具体做法。
Accumulo
中的索引用于查询行
ID
，行
ID
用来读取实际表中的值。让我们来看一个
例子：
SELECT flightnum, origin
FROM flights
WHERE flightdate BETWEEN DATE '2019-10-01' AND '2019-11-05'
AND origin = 'BOS';
在没有索引的情况下，
Trino
会从
Accumulo
中读取整个数据集，然后在 ...
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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.