《数据库英文翻译》word版.docx

《数据库英文翻译》word版.docx

《《数据库英文翻译》word版.docx》由会员分享，可在线阅读，更多相关《《数据库英文翻译》word版.docx（15页珍藏版）》请在冰点文库上搜索。

《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