Prepare for SQL Interview with iQwizz | Difficulty Level: Intermediate | Rating: 4.8

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Question 1

What is a key difference between a regular subquery and a correlated subquery?

Regular subqueries can access columns from the outer query, while correlated subqueries cannot.
Correlated subqueries are executed only once for the entire outer query, while regular subqueries are executed for each row.
Correlated subqueries depend on the outer query for their results, while regular subqueries are independent.
Regular subqueries can modify data, while correlated subqueries are read-only.

Question 2

You're asked to retrieve the names of all employees who earn more than the average salary of their respective departments. This necessitates calculating the average salary per department and then comparing it to individual employee salaries. Which type of subquery would be most appropriate for this scenario?

Inline View
Correlated Subquery
Non-Correlated Subquery
Scalar Subquery

Question 3

Imagine you need to find pairs of employees who share the same job title without displaying the same employee twice (e.g., Employee A paired with Employee B is the same as Employee B with Employee A). Which SQL concept would be most efficient for this task?

Self-Join
INTERSECT
UNION
Cross Join

Question 4

Which of the following SQL statements is used to definitively save changes made within a transaction?

UPDATE
PERSIST
COMMIT
SAVE

Question 5

What is the maximum level of recursion allowed in a recursive CTE?

1,000
10
It depends on the database system's configuration.
100

Question 6

From a table 'Products', retrieve all products whose names start with 'A' or 'B' and end with 'e'.

SELECT *
FROM Products
WHERE ProductName LIKE 'A%e' AND ProductName LIKE 'B%e';

SELECT *
FROM Products
WHERE ProductName BETWEEN 'A' AND 'B' AND ProductName LIKE '%e';

SELECT *
FROM Products
WHERE ProductName LIKE '[AB]%e';

SELECT *
FROM Products
WHERE ProductName LIKE 'A%' OR ProductName LIKE 'B%' AND ProductName LIKE '%e';

Question 7

Which ACID property ensures that any changes made within a transaction are applied to the database in a manner that prevents partial updates, preserving data consistency?

Isolation
Durability
Consistency
Atomicity

Question 8

You are analyzing sales data and want to display the running total of sales for each month. What SQL concept would be MOST suitable for this task?

Window function with SUM() OVER (ORDER BY...)
GROUP BY clause with SUM() aggregate function
Correlated subquery with SUM() function
Self join with aggregate function

Question 9

Which of the following ACID properties ensures that any changes made within a transaction are permanent, even in case of system failures?

Atomicity
Durability
Consistency
Isolation

Question 10

What is the primary purpose of using a Common Table Expression (CTE) in SQL?

To define a recursive relationship within a table.
To replace the need for views in a database.
To create a temporary, named result set that exists only within the scope of the current query.
To improve the performance of complex queries by storing intermediate results.

Please login before attempting the quiz

Question 1

What is a key difference between a regular subquery and a correlated subquery?

Regular subqueries can access columns from the outer query, while correlated subqueries cannot.
Correlated subqueries are executed only once for the entire outer query, while regular subqueries are executed for each row.
Correlated subqueries depend on the outer query for their results, while regular subqueries are independent.
Regular subqueries can modify data, while correlated subqueries are read-only.

Question 2

Inline View
Correlated Subquery
Non-Correlated Subquery
Scalar Subquery

Question 3

Self-Join
INTERSECT
UNION
Cross Join

Question 4

Which of the following SQL statements is used to definitively save changes made within a transaction?

UPDATE
PERSIST
COMMIT
SAVE

Question 5

What is the maximum level of recursion allowed in a recursive CTE?

1,000
10
It depends on the database system's configuration.
100

Question 6

From a table 'Products', retrieve all products whose names start with 'A' or 'B' and end with 'e'.

SELECT *
FROM Products
WHERE ProductName LIKE 'A%e' AND ProductName LIKE 'B%e';

SELECT *
FROM Products
WHERE ProductName BETWEEN 'A' AND 'B' AND ProductName LIKE '%e';

SELECT *
FROM Products
WHERE ProductName LIKE '[AB]%e';

SELECT *
FROM Products
WHERE ProductName LIKE 'A%' OR ProductName LIKE 'B%' AND ProductName LIKE '%e';

Question 7

Which ACID property ensures that any changes made within a transaction are applied to the database in a manner that prevents partial updates, preserving data consistency?

Isolation
Durability
Consistency
Atomicity

Question 8

You are analyzing sales data and want to display the running total of sales for each month. What SQL concept would be MOST suitable for this task?

Window function with SUM() OVER (ORDER BY...)
GROUP BY clause with SUM() aggregate function
Correlated subquery with SUM() function
Self join with aggregate function

Question 9

Which of the following ACID properties ensures that any changes made within a transaction are permanent, even in case of system failures?

Atomicity
Durability
Consistency
Isolation

Question 10

What is the primary purpose of using a Common Table Expression (CTE) in SQL?

To define a recursive relationship within a table.
To replace the need for views in a database.
To create a temporary, named result set that exists only within the scope of the current query.
To improve the performance of complex queries by storing intermediate results.

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