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WHERE EXISTS子查询应用研究 被引量:2
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作者 张艳霞 陈丹琪 韩莹 《电脑知识与技术》 2012年第5期2985-2987,共3页
SELECT语句作为SOL语言的核心,可以通过使用WHERE子句实现灵活而复杂的查询操作。其中,与谓词EXISTS所形成的嵌套查询是理解的难点,该文将通过分析查询实例,探讨如何使用WHERE EXISTS子查询实现复杂的查询操作。
关键词 数据库 SOL exists 子查询
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关系代数中“除法”运算与SQL中带有exists子查询的对比教学 被引量:6
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作者 肖海蓉 《电脑学习》 2009年第3期158-158,F0003,共2页
采用关系代数除法运算与SQL中带有exists子查询的对比教学法,使学生通过实例理解除法运算,加深了对SQL中带有exists子查询的用法,并掌握了两者之间的联系,取得了较好的教学效果。
关键词 关系代数 除法运算 SQL exists子查询
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浅析SQL中WHERE EXISTS子查询 被引量:3
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作者 袁红娟 《长春师范学院学报(自然科学版)》 2006年第3期69-73,共5页
结构化查询语言SQL是一个综合的、通用的、功能极强的关系数据库语言,而SQL语言的核心又是SELECT语句。其中WHERE子句的条件表达式表现得灵活而复杂,与谓词EXISTS所形成的嵌套查询也成为部分人理解的难点,本文将重点剖析WHERE EXISTS子... 结构化查询语言SQL是一个综合的、通用的、功能极强的关系数据库语言,而SQL语言的核心又是SELECT语句。其中WHERE子句的条件表达式表现得灵活而复杂,与谓词EXISTS所形成的嵌套查询也成为部分人理解的难点,本文将重点剖析WHERE EXISTS子查询的语法、执行流程及使用离散数学知识辅助解决复杂查询的实现方法。 展开更多
关键词 数据库 SQL exists 存在量词 全称量词 子查询
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试析SQL中EXISTS关键字的主要作用 被引量:1
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作者 谢从满 《电脑与信息技术》 2015年第5期57-61,共5页
文章给出了在SQL编程中,使用EXISTS关键字完成对空集的判定,实现属于、包含、相等等语义,实现交、差和除等操作的具体方法,包括解题的基本思路、编程的核心步骤以及注意事项等诸多方面,易于理解与学习。针对普遍认为难以处理的具有全称... 文章给出了在SQL编程中,使用EXISTS关键字完成对空集的判定,实现属于、包含、相等等语义,实现交、差和除等操作的具体方法,包括解题的基本思路、编程的核心步骤以及注意事项等诸多方面,易于理解与学习。针对普遍认为难以处理的具有全称量词或包含等语义的编程问题,文中用集合论中的基础知识,给出了一套简洁明了、浅显易懂的解题方法。 展开更多
关键词 SQL exists 集合 包含 除运算
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“EXISTS”在SQL中的应用研究
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作者 肖海蓉 《电脑与电信》 2010年第9期46-48,共3页
为了解决EXISTS在实际使用中的难点,研究了EXISTS的具体应用。同时在SQL Server 2005的环境下,通过实际案例的分析,总结出如何根据实际语义,正确设计出带有EXISTS的SQL查询语句。
关键词 exists SQL SQL SERVER
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Large Potential Exists in China's Oil & Gas Transportation System
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作者 GordonFeller 《China Oil & Gas》 CAS 2002年第3期28-31,共4页
As China in the decades ahead is to go through significant reorganization in the power sector and the petrochemical industry will see considerable growth,the transportation infrastructure for petroleum and gas should ... As China in the decades ahead is to go through significant reorganization in the power sector and the petrochemical industry will see considerable growth,the transportation infrastructure for petroleum and gas should have a new shape. Implementing the largest infrastructure projects and creating on this basis a modern transportation network will not only see a new reincarnation of traditional industrial centers, but also open wider opportunities for regional development. 展开更多
关键词 Large Potential exists in China’s Oil Gas Transportation System LNG Project GAS
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How College Students Suicide Exists: Three Standpoints of Death
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作者 FANG Yajun 《Journal of Philosophy Study》 2020年第12期878-881,共4页
At present,suicide behaviors of college students frequently occur in colleges,but the problem of why college students suicide has always plagued many college educators.From the perspective of Levinas’view of existenc... At present,suicide behaviors of college students frequently occur in colleges,but the problem of why college students suicide has always plagued many college educators.From the perspective of Levinas’view of existence,suicide is the last control that people can have over existence.Suicide includes a person’s three mental states:exhaustion,laziness,and boredom,and it can orderly induce three standpoints of death:“I have to die”,“I want to die”,and“I am going to die”.Knowing the problems of suicide is helpful to help college educators better understand the suicidal behavior of college students and help them better carry out the life education of college students. 展开更多
关键词 college students SUICIDE EXISTENCE DEATH
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Fractal Fractional Order Operators in Computational Techniques for Mathematical Models in Epidemiology 被引量:1
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作者 Muhammad Farman Ali Akgül +2 位作者 Mir Sajjad Hashemi Liliana Guran Amelia Bucur 《Computer Modeling in Engineering & Sciences》 SCIE EI 2024年第2期1385-1403,共19页
New fractional operators, the COVID-19 model has been studied in this paper. By using different numericaltechniques and the time fractional parameters, the mechanical characteristics of the fractional order model arei... New fractional operators, the COVID-19 model has been studied in this paper. By using different numericaltechniques and the time fractional parameters, the mechanical characteristics of the fractional order model areidentified. The uniqueness and existence have been established. Themodel’sUlam-Hyers stability analysis has beenfound. In order to justify the theoretical results, numerical simulations are carried out for the presented methodin the range of fractional order to show the implications of fractional and fractal orders.We applied very effectivenumerical techniques to obtain the solutions of themodel and simulations. Also, we present conditions of existencefor a solution to the proposed epidemicmodel and to calculate the reproduction number in certain state conditionsof the analyzed dynamic system. COVID-19 fractional order model for the case of Wuhan, China, is offered foranalysis with simulations in order to determine the possible efficacy of Coronavirus disease transmission in theCommunity. For this reason, we employed the COVID-19 fractal fractional derivative model in the example ofWuhan, China, with the given beginning conditions. In conclusion, again the mathematical models with fractionaloperators can facilitate the improvement of decision-making for measures to be taken in the management of anepidemic situation. 展开更多
关键词 COVID-19 model fractal-fractional operator Ulam-Hyers stability existence and uniqueness numerical simulation
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Novel Investigation of Stochastic Fractional Differential Equations Measles Model via the White Noise and Global Derivative Operator Depending on Mittag-Leffler Kernel 被引量:1
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作者 Saima Rashid Fahd Jarad 《Computer Modeling in Engineering & Sciences》 SCIE EI 2024年第6期2289-2327,共39页
Because of the features involved with their varied kernels,differential operators relying on convolution formulations have been acknowledged as effective mathematical resources for modeling real-world issues.In this p... Because of the features involved with their varied kernels,differential operators relying on convolution formulations have been acknowledged as effective mathematical resources for modeling real-world issues.In this paper,we constructed a stochastic fractional framework of measles spreading mechanisms with dual medication immunization considering the exponential decay and Mittag-Leffler kernels.In this approach,the overall population was separated into five cohorts.Furthermore,the descriptive behavior of the system was investigated,including prerequisites for the positivity of solutions,invariant domain of the solution,presence and stability of equilibrium points,and sensitivity analysis.We included a stochastic element in every cohort and employed linear growth and Lipschitz criteria to show the existence and uniqueness of solutions.Several numerical simulations for various fractional orders and randomization intensities are illustrated. 展开更多
关键词 Measles epidemic model Atangana-Baleanu Caputo-Fabrizio differential operators existence and uniqueness qualitative analysis Newton interpolating polynomial
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On entire solutions of some Fermat type differential-difference equations
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作者 LONG Jian-ren QIN Da-zhuan 《Applied Mathematics(A Journal of Chinese Universities)》 SCIE CSCD 2024年第1期69-88,共20页
On one hand,we study the existence of transcendental entire solutions with finite order of the Fermat type difference equations.On the other hand,we also investigate the existence and growth of solutions of nonlinear ... On one hand,we study the existence of transcendental entire solutions with finite order of the Fermat type difference equations.On the other hand,we also investigate the existence and growth of solutions of nonlinear differential-difference equations.These results extend and improve some previous in[5,14]. 展开更多
关键词 entire solutions differential-difference equations EXISTENCE finite order
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GLOBAL SOLUTIONS IN THE CRITICAL SOBOLEV SPACE FOR THE LANDAU EQUATION
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作者 Hao WANG 《Acta Mathematica Scientia》 SCIE CSCD 2024年第4期1347-1372,共26页
The Landau equation is studied for hard potential with-2≤γ≤1.Under a perturbation setting,a unique global solution of the Cauchy problem to the Landau equation is established in a critical Sobolev space H_(x)^(d)L_... The Landau equation is studied for hard potential with-2≤γ≤1.Under a perturbation setting,a unique global solution of the Cauchy problem to the Landau equation is established in a critical Sobolev space H_(x)^(d)L_(v)^(2)(d>3/2),which extends the results of[11]in the torus domain to the whole space R_(x)^(3).Here we utilize the pseudo-differential calculus to derive our desired result. 展开更多
关键词 Landau equation nonlinear energy method global existence pseudo-differential calculus
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THE GLOBAL EXISTENCE OF STRONG SOLUTIONS TO THERMOMECHANICAL CUCKER-SMALE-STOKES EQUATIONS IN THE WHOLE DOMAIN
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作者 邹委员 《Acta Mathematica Scientia》 SCIE CSCD 2024年第3期887-908,共22页
We study the global existence and uniqueness of a strong solution to the kinetic thermomechanical Cucker-Smale(for short,TCS) model coupled with Stokes equations in the whole space.The coupled system consists of the k... We study the global existence and uniqueness of a strong solution to the kinetic thermomechanical Cucker-Smale(for short,TCS) model coupled with Stokes equations in the whole space.The coupled system consists of the kinetic TCS equation for a particle ensemble and the Stokes equations for a fluid via a drag force.In this paper,we present a complete analysis of the existence of global-in-time strong solutions to the coupled model without any smallness restrictions on the initial data. 展开更多
关键词 thermomechanical Cucker-Smale model Stokes equations strong solutions global existence
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THE GLOBAL EXISTENCE AND UNIQUENESS OF SMOOTH SOLUTIONS TO A FLUID-PARTICLE INTERACTION MODEL IN THE FLOWING REGIME
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作者 Lin ZHENG Shu WANG 《Acta Mathematica Scientia》 SCIE CSCD 2024年第5期1877-1885,共9页
This paper is concerned with the Cauchy problem for a 3D fluid-particle interaction model in the so-called flowing regime inℝ3.Under the smallness assumption on both the external potential and the initial perturbation... This paper is concerned with the Cauchy problem for a 3D fluid-particle interaction model in the so-called flowing regime inℝ3.Under the smallness assumption on both the external potential and the initial perturbation of the stationary solution in some Sobolev spaces,the existence and uniqueness of global smooth solutions in H3 of the system are established by using the careful energy method. 展开更多
关键词 fluid-particle flowing regime global existence
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Effect of burial depth of a new tunnel on the seismic response of an existing tunnel
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作者 Ma Runbo Cao Qikun +3 位作者 Lu Shasha Zhao Dongxu Zhang Yanan Xu Hong 《Earthquake Engineering and Engineering Vibration》 SCIE EI CSCD 2024年第4期863-882,共20页
Burial depth is a crucial factor affecting the forces and deformation of tunnels during earthquakes.One key issue is a lack of understanding of the effect of a change in the buried depth of a single-side tunnel on the... Burial depth is a crucial factor affecting the forces and deformation of tunnels during earthquakes.One key issue is a lack of understanding of the effect of a change in the buried depth of a single-side tunnel on the seismic response of a double-tunnel system.In this study,shaking table tests were designed and performed based on a tunnel under construction in Dalian,China.Numerical models were established using the equivalent linear method combined with ABAQUS finite element software to analyze the seismic response of the interacting system.The results showed that the amplification coefficient of the soil acceleration did not change evidently with the burial depth of the new tunnel but decreased as the seismic amplitude increased.In addition,the existing tunnel acceleration,earth pressure,and internal force were hardly affected by the change in the burial depth;for the new tunnel,the acceleration and internal force decreased as the burial depth increased,while the earth pressure increased.This shows that the earth pressure distribution in a double-tunnel system is relatively complex and mainly concentrated on the arch spandrel and arch springing of the relative area.Overall,when the horizontal clearance between the center of the two tunnels was more than twice the sum of the radius of the outer edges of the two tunnels,the change in the burial depth of the new tunnel had little effect on the existing one,and the tunnel structure was deemed safe.These results provide a preliminary understanding and reference for the seismic performance of a double-tunnel system. 展开更多
关键词 burial depth new tunnel existing tunnel seismic response shaking table tests numerical simulations
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Stability of second order Hopfield neural networks with time delays
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作者 Wang Shuna Liu Jiang 《江苏师范大学学报(自然科学版)》 CAS 2024年第3期49-55,共7页
Dynamical behaviors of a class of second order Hopfield neural networks with time delays is investigated.The existence of a unique equilibrium point is proved by using Brouwer's fixed point theorem and the counter... Dynamical behaviors of a class of second order Hopfield neural networks with time delays is investigated.The existence of a unique equilibrium point is proved by using Brouwer's fixed point theorem and the counter proof method,and some sufficient conditions for the global asymptotic stability of the equilibrium point are obtained through the combination of a suitable Lyapunov function and an algebraic inequality technique. 展开更多
关键词 Hopfield neural network Lyapunov function existence and uniqueness global asymptotic stability
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具有奇异势和一般非线性的伪抛物方程解的局部存在性和爆破
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作者 江东月 唐忠华 房少梅 《Chinese Quarterly Journal of Mathematics》 2024年第2期111-127,共17页
In this paper,a semilinear pseudo-parabolic equation with a general nonlin-earity and singular potential is considered.We prove the local existence of solution by Galerkin method and contraction mapping theorem.Moreov... In this paper,a semilinear pseudo-parabolic equation with a general nonlin-earity and singular potential is considered.We prove the local existence of solution by Galerkin method and contraction mapping theorem.Moreover,we prove the blow-up of solution and estimate the upper bound of the blow-up time for J(u0)≤0.Finally,we prove the finite time blow-up and estimate the upper bound of blow-up time for J(u0)>0. 展开更多
关键词 Pseudo-parabolic equation Singular potential General nonlinearity Local existence Blow-up time
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The Existence of Solutions for Kirchhoff-Type Equations with General Singular Terms
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作者 WANG Ji-nan SUN Da-wei 《Chinese Quarterly Journal of Mathematics》 2024年第3期315-323,共9页
We study the existence of solutions for Kirchhoff-type equations.Firstly,we use the Sobolev inequality and the weakly lower semi-continuity of the norm to prove that the corresponding function can reach the global min... We study the existence of solutions for Kirchhoff-type equations.Firstly,we use the Sobolev inequality and the weakly lower semi-continuity of the norm to prove that the corresponding function can reach the global minimum.Then,we use the variational method and some analytical techniques to obtain the existence of the positive solution of the equation whenλis small enough. 展开更多
关键词 Kirchhoff-type equation The existence Positive solution Variational method
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一类退化抛物方程高初始能量下解的有限时刻爆破及整体存在性
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作者 刘功伟 杨坤 《Chinese Quarterly Journal of Mathematics》 2024年第1期97-110,共14页
We consider the initial-boundary value problem for finitely degenerate parabolic equation. We first give sufficient conditions for the blow-up and global existence of the parabolic equation at high initial energy leve... We consider the initial-boundary value problem for finitely degenerate parabolic equation. We first give sufficient conditions for the blow-up and global existence of the parabolic equation at high initial energy level. Then, we establish the existence of solutions blowing up in finite time with initial data at arbitrary energy level. Finally, we estimate the upper bound of the blow-up time under certain conditions. 展开更多
关键词 High energy Degenerate parabolic equations Blow up Global existence
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Research on the Development of Smart Animal Husbandry in Beijing
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作者 Yufei JIAO Rao CHEN +3 位作者 Yueyuan ZHAO Yetong WANG Langjiazhuoga Hongjie XU 《Asian Agricultural Research》 2024年第8期6-8,共3页
With the rapid development of agricultural science and technology,animal husbandry,as an important pillar in the field of agriculture,is gradually moving towards a new era of smart animal husbandry with the deep integ... With the rapid development of agricultural science and technology,animal husbandry,as an important pillar in the field of agriculture,is gradually moving towards a new era of smart animal husbandry with the deep integration of informatization and digitalization.This transformation not only breaks through the traditional production mode of animal husbandry,but also promotes it to a new form under the Internet ecology,draws a new blueprint for the development of agriculture and animal husbandry,and gives birth to numerous potential business opportunities for the development of new agriculture.However,the practice and promotion of smart animal husbandry is not a smooth road,and many challenges and problems need to be solved urgently.On the basis of an in-depth investigation of the development status of smart animal husbandry in Beijing,this paper comprehensively analyzes the current problems,including the difficulty of technology integration,the lack of talent reserve,and the need to improve the policy environment.In view of these problems,it puts forward a series of practical suggestions,in order to speed up the development of animal husbandry in Beijing to the direction of smart development,and realize the sustainable development of animal husbandry. 展开更多
关键词 SMART ANIMAL HUSBANDRY SUSTAINABLE DEVELOPMENT Existing problems DEVELOPMENT RECOMMENDATIONS
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Blow-Up and Decay Estimate in a Logarithmic p-Laplace Parabolic Equation
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作者 LI Ping LI Feng-jie 《Chinese Quarterly Journal of Mathematics》 2024年第4期331-354,共24页
This paper deals with an initial-boundary value problem of a fourth-order parabolic equation involving Logarithmic type p-Laplacian,which could be proposed as a model for the epitaxial growth of thin films.By using th... This paper deals with an initial-boundary value problem of a fourth-order parabolic equation involving Logarithmic type p-Laplacian,which could be proposed as a model for the epitaxial growth of thin films.By using the variational method and the logarithmic type Sobolev inequality,we give some threshold results for blow-up solutions and global solutions,which could be classified by the initial energy.The asymptotic estimates about blow-up time and decay estimate of weak solutions are obtained. 展开更多
关键词 High order parabolic equation Blow-up time Decay estimate Global existence Logarithmic type p-Laplacian
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