计算机科学导论课件：databases

Chapter9

DatabasesObjectivesUnderstandaDBMSanddefineitscomponents.UnderstandthearchitectureofaDBMSanditslevels.Distinguishbetweendifferentdatabasemodels.Understandtheconceptofrelationaldatabaseoperationsonarelation.UseStructuredQueryLanguage(SQL)todefinesimplerelations.DatabasesandDBMSAdatabaseisacollectionofdatathatislogically,butnotnecessarilyphysically,coherent.Adatabasemanagementsystemdefines,creates,andmaintainsadatabase.Italsoallowsuserscontrolledaccesstodatainthedatabase.DBMScomponentsDatabasearchitectureDBmodels-hierarchicalDBmodels–networkDBmodel-relationalRelationArelation,inappearance,isatwo-dementionaltable.SQLThestructuredquerylanguageisthestandardizedlanguageweusetooperateonrelationaldatabases.Itisadeclarative(notprocedural)language,whichmeansthattheusersdeclarewhattheywantwithouthavingtowriteastep-by-stepprocedure.Operationsonrelations-insertinsertintoCOURSES

values(“CIS52”,“TCP/IPProtocols”,6)Operationsonrelations-deletedeletefromCOURSES

whereNo=“CIS19”Operationsonrelations-updateupdateCOURSES

setUnit=6

whereNo=“CIS51”Operationsonrelations-selectselect*

fromCOURSES

whereUnit=5Operationsonrelations-projectselectNo,Unit

fromCOURSESOperationsonrelations-joinselectNo,Course-Name,Unit,Professor

fromCOURSES,TAUGHT-BY

whereCOURSES.No=TAUGHT-BY.NoOperationsonrelations-unionselect*

fromCIS15-Roster

unionselect*

fromCIS52-RosterOperationsonrelations-intersectionselect*fromCIS15-Roster

intersection

select*fromCIS52-RosterOperationsonrelations