Quiz for Subqueries in WHERE Clause

Q1: Which of the following is true about subqueries in the WHERE clause?

A. They must be correlated B. They are used for sorting C. They can be used to filter rows based on results of inner queries D. They cannot return values

Q2: What is the purpose of a subquery in the WHERE clause?

A. To filter rows B. To format output C. To join tables D. To create indexes

Q3: Which keyword is used with subqueries in WHERE clause to compare values?

A. EQUALS B. IN C. LIKE D. BETWEEN

Q4: What will the subquery return when used in a WHERE clause?

A. A string B. A number C. A set of values or a single value D. A table

Q5: Which of the following is a correct use of a subquery?

A. WHERE id = (SELECT MAX(id) FROM employees) B. WHERE id LIKE (SELECT name FROM employees) C. WHERE salary BETWEEN (SELECT salary FROM employees) D. WHERE NOT NULL = (SELECT age FROM employees)

Q6: Subqueries in WHERE clause must always return how many rows?

A. One row B. Multiple rows C. It depends on the context D. No rows

Q7: Which SQL clause allows using correlated subqueries?

A. SELECT B. GROUP BY C. WHERE D. HAVING

Q8: Which operator is used to check for existence in a subquery?

A. EXISTS B. IN C. BETWEEN D. ALL

Q9: Which is true about subqueries in WHERE clause?

A. They are executed before the main query B. They are always executed after the main query C. They are executed simultaneously D. They are ignored in execution plan

Q10: What does a scalar subquery return?

A. Multiple rows B. A table C. One value D. Nothing

Q11: What happens if a subquery in WHERE returns multiple rows but = is used?

A. Error B. Warning C. NULL D. All rows returned

Q12: Which clause can include a subquery?

A. WHERE B. FROM C. HAVING D. All of the above

Q13: Which type of subquery depends on the outer query?

A. Independent B. Scalar C. Correlated D. Nested

Q14: Subqueries in WHERE clause can be used with which of the following?

A. =, >, <, IN, EXISTS B. SELECT only C. ORDER BY D. GROUP BY only

Q15: What is the result if a subquery returns NULL?

A. It throws error B. It returns no rows C. It returns all rows D. Depends on condition

Q16: How do you avoid error when subquery returns multiple values?

A. Use IN instead of = B. Use GROUP BY C. Use HAVING clause D. Use ORDER BY

Q17: Which is the correct syntax?

A. SELECT * FROM emp WHERE dept_id IN (SELECT id FROM dept) B. SELECT * WHERE FROM emp (dept_id SELECT) C. SELECT * FROM emp (SELECT id) D. WHERE SELECT FROM emp

Q18: Can a subquery in WHERE clause return a NULL?

A. Yes B. No C. Only if not indexed D. Only in MySQL

Q19: What does the EXISTS operator check for in a subquery?

A. Whether any row is returned B. If table exists C. If column is NULL D. If value is a duplicate

Q20: Can subqueries be nested?

A. Yes, up to one level B. No C. Yes, multiple levels D. Only in SELECT clause

Q21: Why might you use a subquery in WHERE clause?

A. To simplify complex queries B. To increase query time C. To create joins D. To avoid indexes