- A.5
- B.6
- C.7
- D.8
正确答案及解析
正确答案
解析
关系R(A,B,C,D,E)和S(B,C,F,G)做自然连接时,会以两个关系公共字段做等值连接,然后将操作结果集中重复列去除,所以运算后属性列有7个。
接下来分析关系表达式的SQL形式,题目中关系表达式先进行了R与S的自然连接。得到的结果集为:RS(R.A,R.B,R.C,R.D,R.E,S.F,S.G)。此后的选择操作“σ3<6”可表达为“σR.C<S.F”;最后进行投影操作“π1,3,6,7”即选出结果集的第1,3,6,7列,对应的列为:R.A,R.C,S.F,S.G(由于无重复字段,A,C,F,G及A,R.C,F,G或其它等价形式均可)。
包含此试题的试卷
你可能感兴趣的试题
Advancements in ( )have contributed to the growth of the automotive industry through the creation and evolution of self-driving vehicles.
-
- A.Artificial Intelligence
- B.Cloud Computing
- C.Internet of Things
- D.Big Data
- 查看答案
In project human resource management , ( )is not a source of power for the project manager.
-
- A.referent power
- B.expert power
- C.reward power
- D.audit power
- 查看答案
At the project establishment stage , the feasibility study mainly includes techinical feasibility analysis , ( ), operation environment feasibility analysis and other aspects of feasibility analysis.
-
- A.detail feasibility analysis
- B.opportunity analysis
- C.economic feasibility analysis
- D.risk analysis
- 查看答案
( )is a grid that shows the project resources assigned to each work package.
-
- A.Stakeholder engagement assessment matrix
- B.Requirements traceability matrix
- C.Probability and impact matrix
- D.Responsibility assignment matrix
- 查看答案
Xinhua News Agency reported in January 2022,Chian will further promote the developmet of a digital economy during the 14th Five-Year Plan eriod(2021-2025). The plan also emphasized industrial ( )transformation.
-
- A.digital
- B.networking
- C.intelligentize
- D.informatization
- 查看答案