When to use SQL vs NoSQL in HLD - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Choosing the right database for structured data

You have a project that requires storing customer information with fixed fields like name, email, and phone number. Which type of database is best suited for this?

A Use a NoSQL database because it handles fixed fields better.

B Use a SQL database because it is designed for structured data with fixed schemas.

C Use a NoSQL database because it is always faster for any data.

D Use a file system instead of a database for structured data.

💡 Hint

Think about which database type enforces a fixed structure for data.

SQL databases are designed to handle structured data with fixed schemas, making them ideal for customer information with defined fields.

🧠 Conceptual

intermediate

Handling flexible data formats

Your application needs to store user-generated content that can vary in format and fields, such as comments, images, and tags. Which database type fits best?

A SQL database because it handles flexible data well.

B Flat files because they are easier to manage than databases.

C In-memory cache because it stores data permanently.

D NoSQL database because it supports flexible and changing data structures.

💡 Hint

Consider which database type allows storing data without a fixed schema.

NoSQL databases are designed to store flexible and varying data formats, making them suitable for user-generated content with different fields.

❓ query_result

advanced

Querying relational data with SQL

Given a SQL table Orders with columns OrderID, CustomerID, and Amount, what is the result of this query?

SELECT CustomerID, SUM(Amount) AS Total FROM Orders GROUP BY CustomerID;

HLD

SELECT CustomerID, SUM(Amount) AS Total FROM Orders GROUP BY CustomerID;

A A list of customers with the total amount of their orders summed up.

B A list of orders with individual amounts.

C An error because GROUP BY is missing columns.

D A list of customers with the average amount of their orders.

💡 Hint

GROUP BY groups rows by customer and SUM adds amounts per group.

The query groups orders by customer and sums the amounts, returning total spent per customer.

🧠 Conceptual

advanced

Scaling databases for high traffic

Your app expects millions of users and needs to scale horizontally across many servers. Which database type is generally easier to scale horizontally?

A Flat files because they can be copied to many servers easily.

B SQL databases because they are designed for horizontal scaling by default.

C NoSQL databases because they are built to scale horizontally across many servers.

D In-memory databases because they store data on disk.

💡 Hint

Think about which database type is designed for easy distribution across servers.

NoSQL databases are generally designed for horizontal scaling, allowing data to be spread across many servers easily.

🧠 Conceptual

expert

Choosing database type for complex transactions

You need to build a banking system that requires complex transactions with strict consistency and rollback capabilities. Which database type is most suitable?

A SQL database because it supports ACID transactions ensuring consistency.

B NoSQL database because it handles large volumes of data quickly.

C Flat files because they are simple to manage for transactions.

D In-memory cache because it is fast for transactions.

💡 Hint

Consider which database type guarantees transaction safety and consistency.

SQL databases support ACID properties, which are essential for complex transactions requiring consistency and rollback.