《数据库英文翻译》word版.docx
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《数据库英文翻译》word版.docx
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《数据库英文翻译》word版
database
Databaseisinaccordancewiththedatastructuretoorganize,storageandmanagementofdatawarehouse,whicharisesfromfiftyyearsago,withthedatingofinformationtechnologyandthedevelopmentofthemarket,especiallysincethe1990s,datamanagementisnolongermerelydatastorageandmanagement,andtransformedintouserneedsofthevariousdatamanagementway.Thedatabasehasavarietyoftypes,fromthemostsimplestoragehavevariousdataformtocanbecarriedoutmassdatastorageoflargedatabasesystemsareobtainedineachaspecthasextensiveapplication.
Thebirthofdatamanagement
Database'shistorycanbetracedbacktofiftyyearsago,whenthedatamanagementisverysimple.Throughalotofclassification,comparisonandformrenderingmachinerunningmillionsofpunchedCARDSfordataprocessing,itsoperationresultsonpaperprintedorpunchedcardmadenew.Whilethedatamanagementispunchedcardforallthesephysicalstorageandhandling.However,1951yearRemingtonRandcorporation(RemingtonRandInc.)anenzymecalledUnivacIcomputerlaunchedaasecondcaninputhundredsofrecordingtapedrives,whichhascauseddatamanagementrevolution.1956IBMproducethefirstdiskdrives--theRAMACModel305.Thisdriveshave50blanks,eachblanksdiameteris2feet,canstore5MBofdata.Thebiggestadvantageisusediskcanberandomlyaccessdata,andpunchedCARDSandtapecanorderaccessdata.
Databasesystemappearsinthe1960sthebud.Whencomputerbegantowidelyusedindatamanagement,thesharingofdataputforwardmoreandmorehighdemand.Thetraditionalfilesystemalreadycannotsatisfypeople'sneeds.Manageandsharedatacanunifythedatabasemanagementsystem(DBMS)cameintobeing.Thedatamodelisthecoreandfoundationofdatabasesystem,variousDBMSsoftwarearebasedonadatamodel.Sousuallyinaccordancewiththecharacteristicsofthedatamodelandthetraditionaldatabasesystemintomeshdatabase,thehierarchydatabaseandrelationaldatabasethreetypes.
Structuredquerylanguage(SQL)
commercialdatabasesystemsrequireaquerylanguagethatismoreuserfriendly.Inthischapter,westudySQL,themostinfluentialcommerciallymarketedquerylanguage,SQL.SQLusesacombinationofrelational-algebraandrelational-calculusconstructs.AlthoughwerefertotheSQLlanguageasa“querylanguage,”itcandomuchmorethanjustqueryadatabase.Itcandefinethestructureofthedata,modifydatainthedatabase,andspecifysecurityconstraints.Itisnotourintentiontoprovideacompleteusers’guideforSQL.Rather,wepresentSQL’sfundamentalconstructsandconcepts.IndividualimplementationsofSQLmaydifferindetails,ormaysupportonlyasubsetofthefulllanguage.
2.1Background
IBMdevelopedtheoriginalversionofSQLatitsSanJoseResearchLaboratory(now
theAlmadenResearchCenter).IBMimplementedthelanguage,originallycalledSequel,aspartoftheSystemRprojectintheearly1970s.TheSequellanguagehas
evolvedsincethen,anditsnamehaschangedtoSQL(StructuredQueryLanguage).
ManyproductsnowsupporttheSQLlanguage.SQLhasclearlyestablisheditselfas
thestandardrelational-databaselanguage.
In1986,theAmericanNationalStandardsInstitute(ANSI)andtheInternationalOrganizationforStandardization(ISO)publishedanSQLstandard,calledSQL-86.
IBMpublisheditsowncorporateSQLstandard,theSystemsApplicationArchitectureDatabaseInterface(SAA-SQL)in1987.ANSIpublishedanextendedstandardfor
SQL,SQL-89,in1989.ThenextversionofthestandardwasSQL-92standard,andthemostrecentversionisSQL:
1999.Thebibliographicnotesprovidereferencestothesestandards.
Chapter4SQL
Inthischapter,wepresentasurveyofSQL,basedmainlyonthewidelyimplementedSQL-92standard.TheSQL:
1999standardisasupersetoftheSQL-92standard;wecoversomefeaturesofSQL:
1999inthischapter,andprovidemoredetailedcoverageinChapter9.ManydatabasesystemssupportsomeofthenewconstructsinSQL:
1999,althoughcurrentlynodatabasesystemsupportsallthenewconstructs.YoushouldalsobeawarethatsomedatabasesystemsdonotevensupportallthefeaturesofSQL-92,andthatmanydatabasesprovidenonstandardfeaturesthatwedo
notcoverhere.
TheSQLlanguagehasseveralparts:
•Data-definitionlanguage(DDL).TheSQLDDLprovidescommandsfordefiningrelationschemas,deletingrelations,andmodifyingrelationschemas.
•Interactivedata-manipulationlanguage(DML).TheSQLDMLincludesaquerylanguagebasedonboththerelationalalgebraandthetuplerelationalcalculus.Itincludesalsocommandstoinserttuplesinto,deletetuplesfrom,andmodifytuplesinthedatabase.
•Viewdefinition.TheSQLDDLincludescommandsfordefiningviews.
•Transactioncontrol.SQLincludescommandsforspecifyingthebeginningandendingoftransactions.
•EmbeddedSQLanddynamicSQL.EmbeddedanddynamicSQLdefinehowSQLstatementscanbeembeddedwithingeneral-purposeprogramminglanguages,suchasC,C++,Java,PL/I,Cobol,Pascal,andFortran.
•Integrity.TheSQLDDLincludescommandsforspecifyingintegrityconstraintsthatthedatastoredinthedatabasemustsatisfy.Updatesthatviolateintegrityconstraintsaredisallowed.
•Authorization.TheSQLDDLincludescommandsforspecifyingaccessrightstorelationsandviews.
Inthischapter,wecovertheDMLandthebasicDDLfeaturesofSQL.WealsobrieflyoutlineembeddedanddynamicSQL,includingtheODBCandJDBCstandardsforinteractingwithadatabasefromprogramswrittenintheCandJavalanguages.
SQLfeaturessupportingintegrityandauthorizationaredescribedinChapter6,whileChapter9outlinesobject-orientedextensionstoSQL.
Theenterprisethatweuseintheexamplesinthischapter,andlaterchapters,isa
bankingenterprisewiththefollowingrelationschemas:
Branch-schema=(branch-name,branch-city,assets)
Customer-schema=(customer-name,customer-street,customer-city)
Loan-schema=(loan-number,branch-name,amount)
Borrower-schema=(customer-name,loan-number)
Account-schema=(account-number,branch-name,balance)
Depositor-schema=(customer-name,account-number)
Notethatinthischapter,aselsewhereinthetext,weusehyphenatednamesforschema,relations,andattributesforeaseofreading.InactualSQLsystems,however,
hyphensarenotvalidpartsofaname(theyaretreatedastheminusoperator).AsimplewayoftranslatingthenamesweusetovalidSQLnamesistoreplaceallhyphensbytheunderscoresymbol(“”).Forexample,weusebranchnameinplaceof
branch-name.
2.2BasicStructure
Arelationaldatabaseconsistsofacollectionofrelations,eachofwhichisassignedauniquename.EachrelationhasastructuresimilartothatpresentedinChapter3.SQLallowstheuseofnullvaluestoindicatethatthevalueeitherisunknownordoesnotexist.Itallowsausertospecifywhichattributescannotbeassignednullvalues,asweshalldiscussinSection4.11.
ThebasicstructureofanSQLexpressionconsistsofthreeclauses:
select,from,andwhere.
•Theselectclausecorrespondstotheprojectionoperationoftherelationalalgebra.Itisusedtolisttheattributesdesiredintheresultofaquery.
•ThefromclausecorrespondstotheCartesian-productoperationoftherelationalalgebra.Itliststherelationstobescannedintheevaluationoftheexpression.
•Thewhereclausecorrespondstotheselectionpredicateoftherelationalalgebra.Itconsistsofapredicateinvolvingattributesoftherelationsthatappearinthefromclause.
ThatthetermselecthasdifferentmeaninginSQLthanintherelationalalgebraisanunfortunatehistoricalfact.Weemphasizethedifferentinterpretationsheretominimizepotentialconfusion.
AtypicalSQLqueryhastheform
selectA1,A2,...,An
fromr1,r2,...,rm
whereP
EachAirepresentsanattribute,andeachriarelation.Pisapredicate.Thequeryis
equivalenttotherelational-algebraexpression
ΠA1,A2,...,An(σP(r1×r2×···×rm))
Ifthewhereclauseisomitted,thepredicatePistrue.However,unliketheresultofarelational-algebraexpression,theresultoftheSQLquerymaycontainmultiplecopiesofsometuples;weshallreturntothisissueinSection4.2.8.
SQLformstheCartesianproductoftherelationsnamedinthefromclause,performsarelational-algebraselectionusingthewhereclausepredicate,andthenprojectstheresultontotheattributesoftheselectclause.Inpractice,SQLmayconverttheexpressionintoanequivalentformthatcanbeprocessedmoreefficiently.
However,weshalldeferconcernsaboutefficiencytoChapters13and14.
In1974,IBM'sRayBoyceandDonChamberlinwillCoddrelationaldatabase12rulemathematicaldefinitionwithsimplekeywordgrammarexpressioncomesout,putforwardthelandmarkStructuredQueryLanguage(SQL)Language.SQLlanguagefeaturesincludeinquiry,manipulation,definitionandcontrol,isacomprehensive,generalrelationaldatabaselanguage,andatthesametime,ahighlytheprocessoflanguage,onlyrequestusersdonotneedpointedouthowdopointedout.SQLintegrationachieveddatabaseofalllifecycleoperation.SQLdatabaseprovidesandrelationsinteractwiththemethod,itcanworkwithstandardprogramminglanguage.Thedateoftheproduce,SQLlanguagebecamethetouchstoneofinspectionrelationaldatabase,andSQLstandardeveryvariationofguidingtherelationaldatabaseproductdevelopmentdirection.However,untilthetwentiethcentury,themid1970stothetheoryofrelationincommercialdatabaseOracleandSQLusedinDB2.
In1986,theSQLasANSIrelationaldatabaselanguageAmericanstandards,thatsameyearannouncedthestandardSQLt
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