Table Emp(id, dept, salary) has rows (1,’HR’,3000), (2,’IT’,5000), (3,’IT’,4000), (4,’Ops’,2000). SELECT dept FROM Emp GROUP BY dept HAVING MAX(salary) – MIN(salary) > 0; What is returned?
Correct answer D. IT
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Programming MCQs
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A DBA adds an index and moves a table to a faster disk, and no application program or conceptual schema has to change. Which property does this demonstrate?
Correct answer D. Physical data independence
In the three-schema (ANSI/SPARC) architecture, which level describes how a particular group of users sees the data, for example as a view containing only course IDs and enrolment counts?
Correct answer B. External level
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A college keeps a student’s address in separate files for the library and the accounts office, and only the accounts copy is updated after the student moves. Which file-processing problem does this illustrate?
Correct answer A. Data redundancy and inconsistency
Which of the following is a typical function of a database administrator (DBA)?
Correct answer D. Granting users authorisation to access data
Which data model organises records in a tree, so that each child record has exactly one parent record?
Correct answer A. Hierarchical model
In an ER model, Employee has an attribute age that is calculated from the stored attribute date_of_birth. What kind of attribute is age?
Correct answer C. Derived attribute
An employee can have several phone numbers, and the design records all of them against the same employee. In ER terms, what type of attribute is phone_number?
Correct answer C. Multivalued attribute
A weak entity set Dependent is identified through its owner entity Employee. What is the attribute set that distinguishes dependents of the same employee from each other called?
Correct answer A. Discriminator (partial key)
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A bank requires every loan to be linked to at least one customer through the relationship Borrower. How does Loan participate in Borrower?
Correct answer B. Total participation
Each department employs many employees, but each employee works in exactly one department. What is the mapping cardinality from Department to Employee?
Correct answer C. One-to-many
A many-to-many relationship Enrols between Student(student_id) and Course(course_id) has an attribute grade. When mapped to a relational table, what is normally the primary key of Enrols?
Correct answer B. The combination (student_id, course_id)
Which statement best describes a candidate key?
Correct answer C. A minimal superkey, with no proper subset that is also a superkey
When does the finally clause of a try statement execute?
Correct answer D. Always, whether or not an exception occurred in the try block
Which mode should be passed to open() to add text to the end of an existing file without erasing it?
Correct answer C. 'a'
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What happens when open(‘data.txt’, ‘x’) is called and data.txt already exists?
Correct answer C. FileExistsError is raised
What does opening an existing file with mode ‘w’ do to its current contents?
Correct answer D. The contents are erased because the file is truncated
What is the main advantage of using with open(…) as f: to work with a file?
Correct answer A. The file is closed automatically when the block ends, even if an exception occurs
Which two special methods must an object implement to be used as a context manager in a with statement?
Correct answer D. __enter__ and __exit__
In a Python method definition, what does the first parameter, conventionally named self, refer to?
Correct answer B. The instance on which the method was called