已知关系S(S#,Sname,Sage,Sclass), SC(S#,C#,Sc...fad5e0e4a2991749.png

已知关系S(S#,Sname,Sage,Sclass), SC(S#,C#,Score)。如下所示关系代数表达式的含义是________。

中国大学MOOC:已知关系S(S#,Sname,Sage,Sclass),SC(S#,C#,Score)。如下所示关系代数表达式的含义是________。

有学生表Student(S# char(8), Sname char(10), Ssex char(2),Sage integer, D# char(2), Sclass char(6))。若要“检索名字为张某某的所有同学姓名”，SQL语句正确的是_________

有学生表Student(S# char(8), Sname char(10), Ssex char(2), Sage integer, D# char(2), Sclass char(6))。要检索学生表中“所有年龄小于等于19岁的学生的年龄及姓名”，SQL语句正确的是_________

已知有： 学生表Student(S# char(8), Sname char(10), Ssex char(2), Sage integer, D# char(2), Sclass char(6))中，若要在学生表中追加一个元组“学号为98030101的男同学张三，年龄为20，所属系别03，所在班级980301”，则可用：

使用SQL语句，创建各基本表的索引，包括：（1）在表Students的Mno列上按降序创建索引IDX_Stu_Mno（2）在表Courses的Cname列上按升序创建唯一索引IDX_Cou_Cname（3）在表Reports的学年列上按降序，同时在学期列上按升序创建索引（4）在表Teachers的职称列上按升序，同时在出生日期列上按降序创建索引（5）在表Tutors的Tno列上按升序创建索引（6）在表Tutors的Sclass列上按降序创建索引

<spanstyle="display:block;text-align:center;">Cloze5</span>Therewasaveryspecialteacherwhomadeafar-reachingdifferenceinmylife<br/>Fall,1959,thefirstdayofclassatBethesdaChevyChaseHighSchoolwasabouttobegin.“Who”，Iaskedasenior,“isMrs.Mcmara,my10^thgradeEnglishteacher?”Hejust<spanstyle="text-decoration:underline;">&nbsp;1&nbsp;</span>andsaidsomethingaboutmybeingin<spanstyle="text-decoration:underline;">&nbsp;2&nbsp;</span>.Soon,Iunderstoodwhathemeant.Mrs.McNamarahadapatternof<spanstyle="text-decoration:underline;">&nbsp;3&nbsp;</span>thatsherepeatedagainandagain.Wewouldhavealiteraturereadingtaskfor<spanstyle="text-decoration:underline;">&nbsp;4&nbsp;</span>.Thenextday,whenwecametoclass,therewouldbetwoorthreetopicsontheblackboard<spanstyle="text-decoration:underline;">&nbsp;5&nbsp;</span>tothehomeworkreading.Wewere<spanstyle="text-decoration:underline;">&nbsp;6&nbsp;</span>towriteanin–classessayaboutoneofthetopics.Thefollowingday,shewould<spanstyle="text-decoration:underline;">&nbsp;7&nbsp;</span>thecorrectedandgradedessaysandeachpersonwouldbecalled<spanstyle="text-decoration:underline;">&nbsp;8&nbsp;</span>tostandinfrontoftheclassandto<spanstyle="text-decoration:underline;">&nbsp;9&nbsp;</span>his\heressay.Theclasswererequiredtocriticize(评论)thatessay,<spanstyle="text-decoration:underline;">&nbsp;10&nbsp;</span>thegradeofeveryoneinclasswouldbereduced<br/>ThefirsttimethatI<spanstyle="text-decoration:underline;">&nbsp;11&nbsp;</span>herread–write–criticizemethod,Ihadnot<spanstyle="text-decoration:underline;">&nbsp;12&nbsp;</span>todothehomeworkandhadwrittensomethingwithoutknowingwhatitmeant.<spanstyle="text-decoration:underline;">&nbsp;13&nbsp;</span>theextremeembarrassmentIsuffered,standingbeforemyclassmates,<spanstyle="text-decoration:underline;">&nbsp;14&nbsp;</span>myself.Noonelaughedatme,noonewouldbe<spanstyle="text-decoration:underline;">&nbsp;15&nbsp;</span>enough,orfoolishenough,todothatinMrs.McNamara’sclass.Theembarrassmentcamefrom<spanstyle="text-decoration:underline;">&nbsp;16&nbsp;</span>andalongwithitcameastrong<spanstyle="text-decoration:underline;">&nbsp;17&nbsp;</span>nottoletithappenagain.<br/>Mrs.McNamarakeptallofourwrittenworkinfiles;itwaseasytoseethe<spanstyle="text-decoration:underline;">&nbsp;18&nbsp;inwritingthathadoccurred.Whatwasnotsoeasytoseewastheinnertransformationthathadtakenplace,atleastforme.WhatMrs.McNamar&nbsp;19&nbsp;</span>metodowastoseemyselfasothersseemeand,havingdonethat,Icouldimprovemyself.AndI<spanstyle="text-decoration:underline;">&nbsp;20&nbsp;</span>.Thankyou,Mrs.McNamara.<br/>1.A.noddedB.laughedC.apologizedD.shouted<br/>2.A.troubleB.sorrowCdangerD.anger<br/>3.A.behaviorB.evaluationC.activityD.thought<br/>4.A.reviewB.performanceC.practiceD.homework<br/>5.A.addedB.relatedC.contributedD.compared<br/>6.A.expectedB.persuadedC.allowedD.advised<br/>7.A.collectB.returnC.sendD.receive<br/>8.A.onpurposeB.atfirstC.bychanceD.inturn<br/>9.A.talkthroughB.handoverC.readoutD.showoff<br/>10.A.soB.andC.butD.or<br/>11.A.triedB.adoptedC.examinedD.experienced<br/>12.A.undertakenB.attemptedC.botheredD.hesitated<br/>13.A.RememberB.PredictC.BearD.Imagine<br/>14.A.playingjokesonB.makingafoolofC.settingatrapforD.takingadvantageof<br/>15.A.braveB.carelessC.proudD.selfish<br/>16.A.aboveB.withinC.behindD.below<br/>17.A.tendencyB.preferenceC.determinationD.sense<br/>18.A.improvementsB.painsC.difficultiesD.advantages<br/>19.A.trustedB.invitedC.forcedD.permitted<br/>20.A.didB.couldC.hadD.would