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

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Question 1

You're performing a complex transaction and realize you need to undo a portion of the changes made within the current transaction. However, you don't want to roll back the entire transaction. Which SQL feature would allow you to selectively undo a part of the transaction?

ROLLBACK
COMMIT
SAVEPOINT
SET TRANSACTION

Question 2

What is a key advantage of using a subquery in the FROM clause to create a derived table?

It improves the readability of complex queries by breaking them down into smaller, more manageable parts.
It can enhance performance by pre-calculating and storing intermediate results.
It allows you to reuse the derived table multiple times within the same query.
All of the above

Question 3

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

Regular subqueries can modify data, while correlated subqueries are read-only.
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 access columns from the outer query, while correlated subqueries cannot.

Question 4

You are using a correlated subquery to compare values in each row of a table to aggregated data from another table. What is a potential performance concern with this approach?

Correlated subqueries are not recommended for use with aggregated data.
Correlated subqueries can be computationally expensive, especially with large datasets, as the subquery might be executed repeatedly for each row of the outer query.
Correlated subqueries are generally more efficient than joins.
Correlated subqueries can lead to faster data retrieval due to their targeted nature.

Question 5

In SQL, a self-join is used to:

Join a table to itself using an alias.
Improve query performance by reducing the number of joins.
Combine data from multiple tables based on a common column.
Join two tables with different schemas.

Question 6

Which ACID property ensures that a transaction's changes are permanent if it completes successfully, even in the event of a system crash?

Consistency
Atomicity
Durability
Isolation

Question 7

Which of these tools can be used to analyze query performance in SQL?

Data definition language (DDL)
Transaction control language (TCL)
Query optimizer
Query execution plan

Question 8

You need to represent a hierarchical organization structure in a relational database table. Which approach is most suitable for querying and traversing this hierarchical data?

Using multiple tables with foreign key relationships to represent different levels
Storing the entire hierarchy as a single string in a column
Implementing a Recursive CTE to query and navigate the hierarchy
Creating a separate table for each level of the hierarchy

Question 9

What does a clustered index do?

It stores a pointer to the data pages where the indexed values are located.
It improves the performance of all queries on the table.
It creates a copy of the table data, sorted by the indexed column.
It defines the order in which data is physically stored in the table.

Question 10

Which SQL statement is used to discard the changes made within a transaction and revert to the previous state?

DISCARD
UNDO
ROLLBACK
REVERT

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Question 1

ROLLBACK
COMMIT
SAVEPOINT
SET TRANSACTION

Question 2

What is a key advantage of using a subquery in the FROM clause to create a derived table?

It improves the readability of complex queries by breaking them down into smaller, more manageable parts.
It can enhance performance by pre-calculating and storing intermediate results.
It allows you to reuse the derived table multiple times within the same query.
All of the above

Question 3

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

Regular subqueries can modify data, while correlated subqueries are read-only.
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 access columns from the outer query, while correlated subqueries cannot.

Question 4

You are using a correlated subquery to compare values in each row of a table to aggregated data from another table. What is a potential performance concern with this approach?

Correlated subqueries are not recommended for use with aggregated data.
Correlated subqueries can be computationally expensive, especially with large datasets, as the subquery might be executed repeatedly for each row of the outer query.
Correlated subqueries are generally more efficient than joins.
Correlated subqueries can lead to faster data retrieval due to their targeted nature.

Question 5

In SQL, a self-join is used to:

Join a table to itself using an alias.
Improve query performance by reducing the number of joins.
Combine data from multiple tables based on a common column.
Join two tables with different schemas.

Question 6

Which ACID property ensures that a transaction's changes are permanent if it completes successfully, even in the event of a system crash?

Consistency
Atomicity
Durability
Isolation

Question 7

Which of these tools can be used to analyze query performance in SQL?

Data definition language (DDL)
Transaction control language (TCL)
Query optimizer
Query execution plan

Question 8

You need to represent a hierarchical organization structure in a relational database table. Which approach is most suitable for querying and traversing this hierarchical data?

Using multiple tables with foreign key relationships to represent different levels
Storing the entire hierarchy as a single string in a column
Implementing a Recursive CTE to query and navigate the hierarchy
Creating a separate table for each level of the hierarchy

Question 9

What does a clustered index do?

It stores a pointer to the data pages where the indexed values are located.
It improves the performance of all queries on the table.
It creates a copy of the table data, sorted by the indexed column.
It defines the order in which data is physically stored in the table.

Question 10

Which SQL statement is used to discard the changes made within a transaction and revert to the previous state?

DISCARD
UNDO
ROLLBACK
REVERT

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