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1、外文原文IntroductiontoSQLServerBySamuelRelationaldatabaseshavebeenaroundfor30years,buttheywerenottheoriginalkindofdatabase,noraretheythenewestkindofdatabase.XMLandobject-orienteddatastructureshaveevolvedinrecentyears.Butrelationaldatabasesarestillbyfarthemost
2、popularkindofdatabaseavailableandwillbeforsometimetocome.SQListheabbreviationofStructuredQueryLanguageanditisforrelationaldatabases,asthetitleindicatesthisisonlyforfresherwhohasjuststartedthecarrierorwhoiswaitingtoopenupthecarrierintheapplicationprogrammi
3、ngside.ButthatdoesnotmeanthisarticleisatutorialforafresherwhodoesnotknowanythingaboutSQL.ThisarticleismeantforwhoalreadyhavealittleknowledgeinSQLandwanttoimproveit.WhatDoesSQLDo?First,SQListhepremiertoolforviewinginformationfromarelationaldatabase.Itdoesn
4、’tjustgiveyouadatadump.SQLgivesyousophisticatedtoolstosummarize,consolidate,andcalculatefromthedata.Usingtablerelationships,datacanbecombinedfrommultipletablesinanumberofways.Withaproperlydesigneddatabase,SQLcananswerpracticallyanyquestionaboutthedata.Sec
5、ond,SQLprovidescommandstomanipulatethedatainarelationaldatabase.Recordscanbeupdatedandaddedtoordeletedfromatable.HereisSQLasadatabaselanguagereallyshines.Proceduralprogramminglanguages,suchasBASIC,mightrequireseverallinesofcodetoupdatearecordinadatabaseta
6、ble.Inaddition,proceduralprogramminglanguageswouldhavetousesomesortofloopingstructuretorepeatthisprocessoneveryrecord.SQLoperatesonanentiresetofrecordsallatthesametime.SQLislikehaikuforprogrammers;oftenadozenwordsorfewercandeleteorchangethousandsofrecords
7、.Finally,SQLisacompletedatadefinitionlanguage(DDL).Thedatabaseitselfcanbecreatedalongwithalltables,fields,primarykeys,andrelationships.Addtothattherecordinsertcommands,andyoucanhaveacompletedatabaseandallitsdataexpressedinprogrammingcode.Thisgreatlyenhanc
8、esadatabaseprogrammer’sabilitytoworkremotelyortoportdataenhancementsamongvariousinstallations.TheprerequisiteforlearningSQLisknowledgeinDiscreteMathematics(SetTheory,RelationsandFunctions).Althoughitisnotnecessaryto