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数据库理论与技术（2005-06）课程复习题一、选择填空：Recordsinafilemaybevariablelengthbecause（d）a.thesizeofadatafieldwithintherecordmayvaryb.afieldwithintherecordmayberepeatedavariablenumberoftimesc.afieldmayappearinonlysomeoftherecordsd.alloftheabovee.NOAVariablelengthfieldsmeanrecordsarevariablelength.Thishastheconsequencethat(c)-----athebufferpoolmanagermustsupportvariablelengthframes.slot#’scannotbedeterminedasfixedaddressesonthepage,soaslotdirectoryoneachpageisnecessary.differentrecordsfromthesametablecanhavedifferentnumbersoffields.thedifferentfieldsofthesamerecordmustbekeptondifferentpages.B+-treeindexesarenotpossiblefortheserecordsbecausetheorderoftheB+-treecannotbedetermined.Thedifferencebetweenfilesstoringspannedversusunspannedrecordsisthat(e)---aafilewithspannedrecordswilluselessdiskspaceforstoringrecordsthanwithunspannedrecords,ifanintegralnumberofrecordsdonotfitinablockafilewithspannedrecordscanhaverecordsthatarestoredonmorethanonediskblockafilewithspannedrecordsmustbeusedwhenthesizeofarecordislargerthantheblocksizealloftheaboveNOAAnindexisusedinrelationaldatabasesystemsto(b)improvetheefficiencyofnormalizingrelationsimprovetheefficiencyofretrievingrecordsfromarelationimprovetheefficiencyoftheCreateTablestatementbandconlyNOAIndexingtechniquesshouldbeevaluatedonthebasisof:(e)----abcAccesstimeInsertionanddeletiontimeSpaceoverheadaandbonlyAlloftheaboveWhichofthefollowingwouldnotbeconsideredabenefitofindexing?(c)---bToimproveperformanceduringdatasorting.Toinsureuniquenessofkeyvalues.ToavoidreadingtherecordswhenprocessingqueriesthatretrieveonlyindexedcolumnsToimproveperformanceduringlargesequentialtablescans.TohelpqueryoptimizerincostestimationThedifferencebetweenadenseindexandasparseindexisthat(c)---eadenseindexcontainskeysandpointersforasubsetoftherecordswhereasasparseindexcontainskeysandpointersforeveryrecord.adenseindexcanonlybeaprimaryindexwhereasasparseindexcanonlybeasecondaryindex.adenseindexcontainskeysandpointersforeachrecordwh
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