数据库系统概念答案(第五版)

数据库课本答案

CHAPTER2

Exercises

2.4Describethedifferencesinmeaningbetweenthetermsrelationandrelationschema.Answer:Arelationschemaisatypede nition,andarelationisaninstanceofthatschema.Forexample,student(ss#,name)isarelationschemaand

数据库系统概念答案(第五版)

isarelationbasedonthatschema.

2.5ConsidertherelationaldatabaseofFigure2.35,wheretheprimarykeysareun-derlined.Giveanexpressionintherelationalalgebratoexpresseachofthefol-lowingqueries:

a.FindthenamesofallemployeeswhoworkforFirstBankCorporation.b.FindthenamesandcitiesofresidenceofallemployeeswhoworkforFirstBankCorporation.

c.Findthenames,streetaddress,andcitiesofresidenceofallemployeeswhoworkforFirstBankCorporationandearnmorethan$10,000perannum.d.Findthenamesofallemployeesinthisdatabasewholiveinthesamecityasthecompanyforwhichtheywork.

e.Assumethecompaniesmaybelocatedinseveralcities.FindallcompanieslocatedineverycityinwhichSmallBankCorporationislocated.

Answer:

a.Πperson-name(σcompany-name=“FirstBankCorporation”(works))

数据库系统概念答案(第五版)

7

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