In-class Exercise #2 Company Manual Queries
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Questions and Answers

What is the purpose of aggregation functions in SQL?

  • To multiply values in a table
  • To perform operations on groups of rows and return one result per group (correct)
  • To divide values in a table
  • To filter out specific rows from a table

In the given text, which attribute is used for grouping tuples in the aggregation process?

  • Salary
  • Dno (correct)
  • Bdate
  • Employee Fname

What happens if no grouping attribute is specified in an aggregation function?

  • The aggregation function cannot be performed
  • The whole table is treated as one group (correct)
  • Rows with the same value for the grouping attribute are grouped together
  • Each row is considered a separate group

Which of the following statements about aggregation functions in SQL is true?

<p>Aggregation functions can produce one tuple in the result per group (B)</p> Signup and view all the answers

What is the role of the 'Super_ssn' attribute in the provided text?

<p>It identifies the supervisor of an employee (A)</p> Signup and view all the answers

When applying an aggregation function, which attributes survive in the result along with the grouping attributes?

<p>'Dno' attribute and aggregated attribute only (A)</p> Signup and view all the answers

What is the purpose of using aliases in SQL queries?

<p>To give a different name to a relation for convenience (C)</p> Signup and view all the answers

How can aliases be specified in SQL?

<p>Using the AS keyword (C)</p> Signup and view all the answers

What does a missing WHERE-clause in an SQL query indicate?

<p>It indicates a condition of 'WHERE TRUE' (A)</p> Signup and view all the answers

In an SQL query, what is the purpose of retrieving first names for all employees?

<p>To list all employees' first names (B)</p> Signup and view all the answers

How does adding a WHERE clause change the behavior of an SQL query?

<p>It filters the rows returned based on a specific condition (B)</p> Signup and view all the answers

What does using the FROM clause with multiple tables allow in SQL queries?

<p>It combines data from different tables based on a specified condition (A)</p> Signup and view all the answers

How would you retrieve the names of department managers when using the assignment operator?

<p>Rename the Employee table to E_Dept and perform a Cartesian product with the Department table. (B)</p> Signup and view all the answers

What does the operation 'Result ← ϬSSN = MGRSSN (Employee, Department)' in the exercise refer to?

<p>An assignment operation assigning a subset of Employee and Department tables based on SSN and MGRSSN equality. (D)</p> Signup and view all the answers

How can you find all employees (SSN) who do not work on any project manually?

<p>Use a projection operation to select only those employees whose SSNs are not present in the Project table. (C)</p> Signup and view all the answers

What would be the correct way to retrieve the SSN of employees who are neither supervisors nor managers?

<p>Use the set difference operation between all employees and supervisors/managers based on their SSNs. (B)</p> Signup and view all the answers

In what scenario would you use the Rename operation as described in the text?

<p>To adjust column names in a table temporarily for specific operations. (C)</p> Signup and view all the answers

What does the cross product operation involve when used between two tables?

<p>It creates a new table with all possible combinations of rows from both input tables. (C)</p> Signup and view all the answers

What is the purpose of the SELECT statement in SQL?

<p>To retrieve attribute values from a database (D)</p> Signup and view all the answers

What is the function of the WHERE clause in a SQL query?

<p>To identify the tuples to be retrieved based on a condition (A)</p> Signup and view all the answers

How can SQL tables be constrained to be sets?

<p>By using the DISTINCT option in a query (C)</p> Signup and view all the answers

What is the purpose of specifying PRIMARY KEY or UNIQUE attributes in SQL tables?

<p>To prevent duplicate values in the specified attribute(s) (D)</p> Signup and view all the answers

In SQL, what does the DISTINCT option do in a query?

<p>Retrieves all attribute values without duplicates (D)</p> Signup and view all the answers

What does the PREFIX TableName.AttributeName indicate in SQL?

<p>It resolves naming conflicts for attributes with the same name (C)</p> Signup and view all the answers

What value does Sally see in the database if she executes her statements after (ins) but before the rollback?

<p>3.50 (D)</p> Signup and view all the answers

What happens to the effects of a transaction if it executes ROLLBACK instead of COMMIT?

<p>Its effects can never be seen (B)</p> Signup and view all the answers

What does SET TRANSACTION ISOLATION LEVEL allow within a transaction?

<p>Selection of the isolation level for the transaction (A)</p> Signup and view all the answers

In SERIALIZABLE isolation level, what does Sally see regarding Joe's transaction?

<p>Database state before or after Joe's transaction, but not within (D)</p> Signup and view all the answers

What is the purpose of isolation levels in SQL transactions?

<p>To control which interactions are allowed by concurrent transactions (D)</p> Signup and view all the answers

How does the DBMS handle isolation levels concerning the visibility of transactions?

<p>By providing its own implementation options (C)</p> Signup and view all the answers

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