March 2021
Intermediate to advanced
265 pages
6h 50m
Chinese
Content preview from Presto实战
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164
｜
第
9
章
函 数 返回类型 描 述
current_timestamp or now() TIMESTAMP WITH TIME ZONE
返回当前时间、日期和时区
localtime TIME
基于本地时区返回当前时间
localtimestamp TIMESTAMP
基于本地时区返回当前的日期和时间
from_unixtime(unixtime) TIMESTAMP
将一个
UNIX
时间转换为日期和时间
to_unixtime(timestamp) DOUBLE
将日期和时间转换为
UNIX
时间值
to_milliseconds(interval) BIGINT
将时间间隔转换为毫秒
9.17
直方图
Presto
提供了
width_bucket
函数用来创建等宽
直方图
。
width_bucket(
x, bound1, bound2, n
) -> bigint
表达式
x
表示用来创建直方图的数值。等宽直方图包含
n
个桶，并使用
bound1
和
bound2
作为值的界限。该函数返回表达式
x
的每个值对应的桶编号。
让我们以航班数据集为例，计算出从
2010
年到
2020
年
10
年内的直方图：
SELECT count(*) count, year, width_bucket(year, 2010, 2020, 4) bucket
FROM flights_orc
WHERE year >= 2010
GROUP BY year;
count | year | bucket
---------+------+-------- ...
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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.