March 2021
Intermediate to advanced
265 pages
6h 50m
Chinese
Content preview from Presto实战
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150
｜
第
9
章
9.3
布尔运算符
布尔运算符
是双目运算符，在
SQL
中用于比较两个操作数的值
，从而产生
TRUE
、
FALSE
或
NULL
的布尔型结果。这些运算符（见表
9-1
）最常用于
WHERE
、
HAVING
或
ON
等条件子句。
可以在查询中任何能够使用表达式的地方使用它们。
表9-1：布尔运算符
运 算 符 描 述
<
小于
<=
小于等于
>
大于
>=
大于等于
=
相等
<>
不相等
!=
不相等
语法
!=
不属于标准
SQL
，但在各种编程语言中普遍使用。许多流行的数据
库中也有实现，因此在
Presto
中也提供了这个语法以方便使用。
下面是一些布尔运算符的使用示例。
2
月某周中飞离波士顿最佳日子是哪一天？
SELECT dayofweek, avg(depdelayminutes) AS delay
FROM flights_orc
WHERE month = 2 AND origincityname LIKE '%Boston%'
GROUP BY dayofweek
ORDER BY dayofweek;
dayofweek | delay
-----------+--------------------
1 | 10.613156692553677
2 | 9.97405624214174
3 | 9.548045977011494
4 | 11.822725778003647
5 | 15.875475113122173
6 | 11.184173669467787
7 | 10.788121285791464 ...
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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.