Quiz for Subqueries in SELECT Clause

Q1: What is the purpose of using a subquery inside the SELECT clause?

A. To filter the rows B. To compute a value per row C. To join tables D. To limit the result

Q2: What is a subquery in a SELECT clause commonly used for?

A. To compute derived columns B. To filter rows C. To insert data D. To update records

Q3: Which keyword is mandatory for writing a subquery in the SELECT clause?

A. FROM B. AS C. INTO D. OUTER

Q4: What is required when using a scalar subquery in the SELECT clause?

A. The subquery must return only one row and one column B. The subquery must return multiple rows C. The subquery must update a value D. The subquery must contain a JOIN

Q5: Which of the following is true about subqueries in the SELECT clause?

A. They can be used for aggregation B. They replace the FROM clause C. They create new tables D. They are used only in joins

Q6: What happens if a subquery in a SELECT clause returns multiple rows?

A. It causes an error B. It returns NULL C. It selects the first row D. It performs a join

Q7: Can a subquery in SELECT clause use aggregation functions like SUM or AVG?

A. Yes B. No C. Only SUM D. Only in WHERE clause

Q8: Which of the following is a valid usage of subquery in SELECT?

A. SELECT name, (SELECT MAX(salary) FROM employee) AS max_salary FROM department; B. SELECT * FROM (SELECT name FROM employee); C. SELECT (FROM employee) name; D. SELECT name IN (SELECT salary FROM employee);

Q9: Can you use a correlated subquery in the SELECT clause?

A. Yes B. No C. Only in PostgreSQL D. Only in WHERE clause

Q10: What does the alias in a subquery help with?

A. Naming the derived column B. Updating rows C. Filtering data D. Dropping tables

Q11: Which of the following errors occurs when subquery returns more than one row in SELECT?

A. Subquery returns more than one row B. Syntax Error C. Permission Denied D. Ambiguous Column

Q12: Which clause can you NOT use a subquery in?

A. ORDER BY B. WHERE C. FROM D. SELECT

Q13: What kind of value is expected from a SELECT subquery?

A. Scalar value B. Table C. Boolean D. Array

Q14: Which SQL clause allows subqueries to be used in computing per-row data?

A. SELECT B. GROUP BY C. ORDER BY D. DROP

Q15: In SELECT clause, subqueries are usually used for:

A. Derived columns B. Defining indexes C. Creating triggers D. Modifying procedures

Q16: What is a derived column?

A. A column computed using a subquery B. A column from another table C. A renamed primary key D. A null value

Q17: Can you nest subqueries inside subqueries in a SELECT clause?

A. Yes B. No C. Only in joins D. Only in triggers

Q18: Which SQL function is often used with subqueries in SELECT?

A. AVG B. TRUNCATE C. INSERT D. ROLLBACK

Q19: How do you alias the result of a subquery in SELECT?

A. Using AS keyword B. Using JOIN C. Using ON clause D. Using INTO

Q20: What happens if alias is not provided to a subquery result in SELECT?

A. DBMS-specific behavior or error B. Syntax error in all cases C. Null result D. Duplicate rows

Q21: Why should you be careful with correlated subqueries in SELECT?

A. They can slow down performance B. They are not supported C. They delete data D. They affect triggers