having是啥意思?
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v. 有; 持有; 占有; 由…组成; 显示出,带有(性质、特征);
一、发音
having 英[ˈhævɪŋ];美[ˈhævɪŋ]
二、用法
1、动词have的现在分词形式
2、(复)havings: 所有财产
三、例句
It's time for having a rest.
该休息一会儿了。
扩展资料:
原型:have
一、发音
英 [həv];美 [həv]
二、含义
vt. 有;吃;得到;从事;允许;雇用;享有
n. [常用复数]富人,有产者,有钱人;富国
三、用法
1、have用作助动词时,可与动词的过去分词或“been+现在分词”连用,构成动词的各种完成时态。
2、have的过去分词had还可与主语倒置,构成虚拟条件状语从句。
四、例句
A country must have the will to repel any invader.
一个国家得有决心击退任何入侵者。
参考技术Ahaving
英 ['hævɪŋ] 美 ['hæviŋ]
n. 所有;持有;占有
v. 有(have的ing形式)
adj. 具有的;所有的
例句:
The staff was drooling over having a day off.
全体职员对有一天休假表示兴高采烈。
The advantages of having a TV set and the money it costs balance each other out.
拥有一台电视机的优越性与购买它所需的钱财相互抵消。
Our two peoples share the same experience of having been oppressed by imperialism.
我们两国人民都有遭受帝国主义压迫的共同经历。
I'm having a party next Saturday;put it down in your notebook so you will not forget it.
本星期六我有个聚会,把这事记在你的笔记本上以免忘记。
Any car having a dangerous problem should be black-flagged instantly.
有危险问题的赛车应即停车受检。
关系代数中 Group By 和 Have 子句查询的等价物是啥?
【中文标题】关系代数中 Group By 和 Have 子句查询的等价物是啥?【英文标题】:What is the equivalent for a Group By and Having clause query in Relational Algebra?关系代数中 Group By 和 Have 子句查询的等价物是什么? 【发布时间】:2012-05-05 16:33:43 【问题描述】:示例:
7.查找同一天拜访过同一专业的两位不同医生的患者。
SELECT p.pid , d.speciality, v.date
FROM Patient p
JOIN Visits v ON v.pid = p.pid
JOIN Doctors d ON d.did = v.did
GROUP BY p.pname, d.speciality, v.date
HAVING COUNT(DISTINCT d.did) = 2
您如何为此编写合法的 RA?
RA 中 GroupBy 和 Have 子句基本上是什么等价的?
同样被问到但没有得到回答here
【问题讨论】:
查看@onedaywhen 的评论,在他的回答下:Converting aggregate operators from SQL to relational algebra 【参考方案1】:您实际上不需要尝试转换 SQL,反映问题也提供了 RA 解决方案:
“查找同一天拜访过同一专业的两位不同医生的患者”
我们首先将患者、就诊和医生结合起来
Patients x Visits x Doctors
由于我们有两次就诊和两名医生,我们需要另一个表访问和医生的实例。我们不能照原样使用它们,否则我们将无法区分它们。因此,重命名\rho
:
Patients x \rho_V1(Visits) x \rho_D1(Doctors) x \rho_V2(Visits) x \rho_D2(Doctors)
接下来我们需要选择“匹配”的组合
\sigma_Patients.pid = V1.pid /\
Patients.pid = V2.pid /\
V1.date = V2.date /\
V1.did = D1.did /\
V2.did = D2.did /\
D1.did != D2.did /\
D1.speciality = D2.speciality
(Patients x \rho_V1(Visits) x \rho_D1(Doctors) x
\rho_V2(Visits) x \rho_D2(Doctors))
接下来我们需要找到患者,即pid
上的项目
\pi_Patients.pid
(\sigma_Patients.pid = V1.pid /\
Patients.pid = V2.pid /\
V1.date = V2.date /\
V1.did = D1.did /\
V2.did = D2.did /\
D1.did != D2.did /\
D1.speciality = D2.speciality
(Patients x \rho_V1(Visits) x \rho_D1(Doctors) x
\rho_V2(Visits) x \rho_D2(Doctors)))
通过这种方式,您找到了在同一天拜访了至少位同一专业的两位不同医生的患者。如果您需要找到那些恰好访问过两位医生的患者,您应该记住恰好 2 = 至少 2 - 至少 3,即,
\pi_Patients.pid
(\sigma_Patients.pid = V1.pid /\
Patients.pid = V2.pid /\
V1.date = V2.date /\
V1.did = D1.did /\
V2.did = D2.did /\
D1.did != D2.did /\
D1.speciality = D2.speciality
(Patients x \rho_V1(Visits) x \rho_D1(Doctors) x
\rho_V2(Visits) x \rho_D2(Doctors)))
-
\pi_Patients.pid
(\sigma_Patients.pid = V1.pid /\
Patients.pid = V2.pid /\
Paitents.pid = V3.pid /\
V1.date = V2.date /\
V2.date = V3.date /\
V1.did = D1.did /\
V2.did = D2.did /\
V3.did = D3.did /\
D1.did != D2.did /\
D1.did != D3.did /\
D2.did != D3.did /\
D1.speciality = D2.speciality /\
D2.speciality = D3.speciality
(Patients x \rho_V1(Visits) x \rho_D1(Doctors) x
\rho_V2(Visits) x \rho_D2(Doctors) x
\rho_V3(Visits) x \rho_D3(Doctors) ))
【讨论】:
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