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1、外文原文IntroductiontoSQLServerBySamuelRelationaldatabaseshavebeenaroundfor30years,buttheywerenottheoriginalkindofdatabase,noraretheythenewestkindofdatabase.XMLandobject-orienteddatastructureshaveevolvedinrecentyears.Butrelationaldatabasesarestillbyfarthemostpopularkindofdatabaseavailableandwillbefor
2、sometimetocome.SQListheabbreviationofStructuredQueryLanguageanditisforrelationaldatabases,asthetitleindicatesthisisonlyforfresherwhohasjuststartedthecarrierorwhoiswaitingtoopenupthecarrierintheapplicationprogrammingside.Butthatdoesnotmeanthisarticleisatutorialforafresherwhodoesnotknowanythingabou
3、tSQL.ThisarticleismeantforwhoalreadyhavealittleknowledgeinSQLandwanttoimproveit.WhatDoesSQLDo?First,SQListhepremiertoolforviewinginformationfromarelationaldatabase.Itdoesn’tjustgiveyouadatadump.SQLgivesyousophisticatedtoolstosummarize,consolidate,andcalculatefromthedata.Usingtablerelationships,da
4、tacanbecombinedfrommultipletablesinanumberofways.Withaproperlydesigneddatabase,SQLcananswerpracticallyanyquestionaboutthedata.Second,SQLprovidescommandstomanipulatethedatainarelationaldatabase.Recordscanbeupdatedandaddedtoordeletedfromatable.HereisSQLasadatabaselanguagereallyshines.Proceduralprog
5、ramminglanguages,suchasBASIC,mightrequireseverallinesofcodetoupdatearecordinadatabasetable.Inaddition,proceduralprogramminglanguageswouldhavetousesomesortofloopingstructuretorepeatthisprocessoneveryrecord.SQLoperatesonanentiresetofrecordsallatthesametime.SQLislikehaikuforprogrammers;oftenadozenwo
6、rdsorfewercandeleteorchangethousandsofrecords.Finally,SQLisacompletedatadefinitionlanguage(DDL).Thedatabaseitselfcanbecreatedalongwithalltables,fields,primarykeys,andrelationships.Addtothattherecordinsertcommands,andyoucanhaveacompletedatabaseandallitsdataexpressedinprogrammingcode.Thisgreatlyenh
7、ancesadatabaseprogrammer’sabilitytoworkremotelyortoportdataenhancementsamongvariousinstallations.TheprerequisiteforlearningSQLisknowledgeinDiscreteMathematics(SetTheory,RelationsandFunctions).Althoughitisnotnecessaryto