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3 years ago

Consider the following relational schema, where the primary keys are Bold,

Computers and Technology

1 answer:

sp2606 [1]3 years ago

5 0

Answer:

The queries for each question are explained.

1. Find the sids and snames of students who took "Database" course (i.e., cname = ‘Database’) in Fall 2019.

The columns sid and sname are taken from students table.

The course name belong to the courses table.

The semester and year belong to the grades table.

To get the final query, all these tables need to be joined in the FROM clause using JOIN ON keywords.

select s.sid, sname

from students s join grades g on g.sid = s.sid

join courses c on g.cid = c.cid

where cname like 'database%'

and semester like 'Fall'

and year=2019

2. Find the average grade of all the students who took "CS327" (i.e., cid=‘CS327’) in Fall 2019. You can assume grade is a numerical attribute.

The grade column is taken from grades table.

The course id belongs to the grades table.

The semester and year also belong to the grades table.

The final query is formed using the grades table only.

select avg(grade)

from grades

where cid like 'CS327'

and semester like 'Fall'

and year=2019

3. Find the number of distinct courses offered by each department in Fall 2019.

The department id belongs to the courses table.

The course id belongs to the grades table.

The semester and year also belong to the grades table.

To get the final query, the courses and the grades tables are joined in the FROM clause using JOIN ON keywords.

select dept_id, count(distinct g.cid)

from courses c join grades g on c.cid = g.cid

where semester like 'Fall'

and year=2019

group by dept_id

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Answer:

A Trojan

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4 years ago

Selet the correct answer.

diamong [38]

Answer:

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3 years ago

Read 2 more answers

Exactly how thin is the air in outer space?

Nata [24]

There is no air in space i is just a void.

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4 years ago

Write a program that defines an interface having the following methods: addition, subtraction, multiplication, and division. Cre

Tatiana [17]

Hello, you haven't provided the programing language in which you need the code, I'll explain how to do it using Python, and you can follow the same logic to make a program in the programing language that you need.

Answer:

1. # -*- coding: utf-8 -*-

2. #Python

3. class Calculator:

4. def add(self):

5. print(a + b)

6. def sub(self):

7. print(a - b)

8. def mul(self):

9. print(a * b)

10. def div(self):

11. print(a / b)

12.

13. obj = Calculator()

14. choice = 1

15. while choice != 0:

16. a = int(input("\nEnter first number: "))

17. b = int(input("Enter first number: "))

18.

19. print("\n0. EXIT")

20. print("1. DIVISION")

21. print("2. ADDITION")

22. print("3. SUBTRACTION")

23. print("4. MULTIPLICATION")

24.

25. choice = int(input("\nEnter your choice: "))

26. if choice == 1:

27. obj.div()

28. elif choice == 2:

29. obj.add()

30. elif choice == 3:

31. obj.sub()

32. elif choice == 4:

33. obj.mul()

34. else:

35. break

Explanation:

From lines 1 to 12 we define the object with four methods, addition, subtraction, multiplication, and division. Each method contains the operation between two variables inside a print function
On line 13 we instantiate our class
On line 14 we declare the variable choice that is going to store the operation that the user wants to perform
On line 15 we declare a while loop, this is going to keep running the program until the user wants to exit
From line 16 to 18 we ask the user to enter two numbers
From line 19 to 24 we print the possible operation, assigning a number for each operation, this indicates to the user what number to press for what operation
On line 25 we ask the user for the operation
From lines 26 to 35 we check the user input an accordingly we call the corresponding method to performs the operation

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3 years ago

Complete the firstMiddleLast() function to return a new string with the first, middle, and last character from string. If string

morpeh [17]

public static void main()

{

String s = Console.ReadLine();

int len = s.length();

Char startletter = s[0];

Char endletter = s[len-1];

string midletter = ‘’;

if(len % 2 ==0)

midletter = s[len/2] + s[(len/2) +1]

else

midletter = s[len/2];

Console.WriteLine(startletter + midletter + endletter);

}

Here the logic is that, startletter is obtained using the index ‘0’, the last letter is obtained by calculating the “length of the string” and subtract 1 to get the “last index” of the given string.

Middle letter is calculated by first finding whether the given string length is “odd or even” and based on that index(es) are identified.

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3 years ago