题目内容
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[单选题]
The relational data model is proposed by :
A.C. W. Bachman
B.R. Boyce
C.E. F. Codd
D.J. Gray
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发布时间：2022-01-07
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A、convoyed
B、surpassed
C、conquered
D、invaded
题目内容
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In 1812 the French army _____ Russia but never got further than Moscow and had to turn back.
第2题
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You'd better bring an【46】license, although non-U.S. licenses are acceptable.
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第6题
Natural join is an additional operation in relational algebra, it can be replaced by which set of the following operations equivalently :
A、Select, Project
B、Cartesian-Product, Project
C、Cartesian-Product, Select, Project
D、Cartesian-Product, Select
第7题
Division is an additional operation in relational algebra, it can be replaced by which set of the following operations equivalently :
A、Select, Project, Cartesian-Product
B、Union, Project, Cartesian-Product
C、Select, Rename, Cartesian-Product
D、Set difference, Project, Cartesian-Product
第8题
Which of the following is WRONG in the relation rules?
A、There is no order on the rows.
B、There is no order on the columns.
C、Two tuples can be identical in all column values.
D、Multi-valued attributes are not permitted.
第9题
The constraint “In a base relation, NO attribute of a primary key can be null”, is called :
A、Entity integrity
B、Referential integrity
C、Check constraint
D、User defined constraint
