【判断题】这种不爱惜劳动成果、任意浪费,是可耻的。
【单选题】下列哪一项最可能导致生产可能性曲线向外移动()
【单选题】In the relational algebra θρ(r), ρ is called ( ).
【单选题】The symbol ρ is a ( ) operator in relational algebra.
【单选题】Divisionis 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
【简答题】The result of a relational-algebra
operation is ().A. relation B. tuple C. field D. keyword
【判断题】The operator ( ) associates every tuple of two tables in relational algebra.A. ∏ B. × C. θ D. ρ
【单选题】Natural join is an additional operation in relational algebra, it can be replaced by which set of the following operations equivalently :
B.
Cartesian-Product, Project
C.
Cartesian-Product, Select, Project
D.
Cartesian-Product, Select