Multiple choice
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Regarding the database system, the following statement is correct.
A. The composition of database system includes computer/network basic system, database and database management system
B. The composition of database system includes computer/network basic system, database, database management system and database application program
C. The composition of database system includes computer/network Basic systems, databases, database applications, and database administrators
D. The composition of the database system includes databases, database management systems, database applications, database administrators, and basic computer and network systems -
Which of the following functions is not a function of the database management system __________.
A. Concurrency control
B. Integrity control
C. CPU control
D. Failure recovery -
In the three-level mode and two-level image architecture of the database, the "global mode" refers to __________.
A. User mode
B. Internal mode
C. Conceptual model
D. Outer mode
Book P5
- Regarding data independence, the following statement is correct as __________.
A. The mapping from the outer mode to the inner mode realizes the physical independence of the data
B. The mapping from the outer mode to the conceptual mode realizes the physical independence of the data
The mapping of C conceptual mode to inner mode realizes the physical independence of data
D. None of the above statements are correct
Book P5
- The collection of information stored in the database at a specific time is called a _______________ of the database.
A. Physical mode
B. Logical mode
C. Sub-mode
D. Examples
Book P5
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Which of the following statements is correct is _______.
A. R(A1, A2,…, An ), this description is also known as the relational mode, where Ai refers to the domain corresponding to the attribute
B. The relational mode and the relational instance are not changed over time
C. The same relational mode The next relationship instance is unique
D. Two identical columns are not allowed in the relational table -
Regarding student relations, which of the following attributes is suitable as a candidate code _______.
A. Age
B. Gender
C. Student ID
D. Class -
In the relational model, which of the following statements about candidate codes is correct is _______.
A. Can be composed of multiple arbitrary attributes
B. At most, composed of one attribute whose value can uniquely identify any tuple of the relationship
C. It can be composed of one or more attributes whose value can uniquely identify any tuple in the relationship
D. None of the rest -
In the relational model, the association between different relations is achieved through ________.
A. Domain
B. Tuple
C. Candidate code
D. Outer code -
Which of the following operations is not a basic relational algebra operation ______.
A. Choose
B. and
C. Hand in
D. Cartesian product
The five basic relational algebra operations are: union, difference, Cartesian product, projection and selection;
- Expressions "extract rows that meet certain conditions from all rows of a relationship", "extract certain columns from all columns of a relationship", "extract all tuples that belong to one relationship but do not belong to another relationship" "The order of operations is __________.
1. Choose 2, Project 3, Union 4, Difference 5, Cartesian Product
A. 1、2、3
B. 1、2、4
C. 2、3、4
D. 1、2、5
12. Natural connection is an effective way to form a new relationship. In general, when using natural connections for the relations R and S, it is required that R and S contain one or more _______ in common.
A. Tuples
B. Properties
C. Main code
D. Foreign code
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Suppose the number of attributes of the relations R and S are n and m, respectively, then the number of attributes of the R×S operation result is ________.
A. n×m
B. n+m
C. n-m
D. max(n,m) -
Suppose the relations R, S, and W each have 10 tuples, then the number of tuples of the Cartesian product of these three relations is _________.
A. 10
B. 30
C. 1000
D. Not sure -
Assuming that the relationship R and the relationship S have the same number of attributes, and the values of the corresponding attributes are taken from the same domain, then R-(RS) is equal to _________.
A. R∩S
B. R∪S
C. S – R
D. S -
The following statement is correct __________.
A. The results of the R∪S and S∪R operations are not the same relationship
B. The results of the R-S and S-R operations are the same relationship
C. The result of R x S and S x R operations is the same relationship
D. Other claims are wrong -
Known student relationship S (student number S#, name Sname, age Sage), elective relationship SC (student number S#, course number C#, score Score). The meaning of the following relational algebraic expression is ________.
A. Query the name and age of the students who
have taken the course number "002" B. Query the name and age of the students who have not taken the course number "002"
C. Query not only the number of the students who have taken the course number "002" Name and age of the student
D. Everything else is wrong -
Known student relationship S (student number S#, name Sname, gender Ssex), course relationship C (course number C#, course name Cname, teacher Cteacher), elective relationship SC (student number S#, course number C#, score Score) , To find the names of female students who have taken the "COMPUTER" course, the correct relational algebra expression is ________.
A.
B.
C.
D. Everything else is wrong -
According to the following relationship, find the result of table R⋈W_______.
R
W
A.
B.
C.
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The student relationship R is shown in the following figure. Use relational algebra to query the student ID and name of all students who are studying in the "03" department and whose age is less than 21. The correct expression is ________.
A.
B.
C.
D.
