NoSQL vs relational database comparison in DynamoDB - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Primary difference between NoSQL and relational databases

Which statement best describes the main difference between NoSQL databases like DynamoDB and traditional relational databases?

A Relational databases use structured query language (SQL) and fixed schemas, while NoSQL databases like DynamoDB use flexible schemas and key-value or document models.

B Relational databases are designed only for unstructured data, while NoSQL databases handle only structured data.

C NoSQL databases store data in tables with fixed schemas, while relational databases store data as flexible documents.

D NoSQL databases require complex joins for queries, whereas relational databases do not support joins.

💡 Hint

Think about how data is organized and queried in each type.

Relational databases use fixed schemas and SQL for structured data, while NoSQL databases like DynamoDB use flexible schemas and store data as key-value or documents.

❓ query_result

intermediate

DynamoDB query output for a simple key lookup

Given a DynamoDB table named Users with primary key UserID, what will be the output of this query?

SELECT * FROM Users WHERE UserID = '123'

Assuming the table has one item with UserID '123' and attributes Name: 'Alice', Age: 30.

A [{"UserID": 123, "Name": "Alice", "Age": "30"}]

B SyntaxError: DynamoDB does not support SQL queries

C []

D [{"UserID": "123", "Name": "Alice", "Age": 30}]

💡 Hint

Consider the data types and the query result format.

The query returns the item with UserID '123' including all attributes. The UserID is a string, Age is a number.

📝 Syntax

advanced

Identify the error in this DynamoDB update expression

What error will this DynamoDB update expression cause?

UpdateExpression: "SET Age = Age + :val"
ExpressionAttributeValues: {":val": 1}

A SyntaxError: Missing colon in ExpressionAttributeValues key

B ValidationException: Cannot increment a non-numeric attribute

C No error; the update will increment Age by 1

D TypeError: ExpressionAttributeValues must be a list

💡 Hint

Think about the data type of the attribute being updated.

If Age is not a number, DynamoDB will raise a ValidationException when trying to increment it.

❓ optimization

advanced

Best practice for querying large datasets in DynamoDB

You want to retrieve all items from a DynamoDB table with millions of records. Which approach is best to optimize performance and cost?

A Export the entire table to S3 and query using SQL there.

B Use a Scan operation with no filters to get all items at once.

C Use Query operations with appropriate partition keys and apply filters to reduce data scanned.

D Use multiple parallel Scan operations without pagination.

💡 Hint

Consider how DynamoDB charges and performs scans vs queries.

Query operations with partition keys are efficient and cost-effective compared to full table scans.

🔧 Debug

expert

Why does this relational join query fail on DynamoDB?

Consider this SQL query:

SELECT Orders.OrderID, Customers.Name FROM Orders JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

Why will this query fail or not work as expected in DynamoDB?

A DynamoDB does not support JOIN operations natively; data must be denormalized or joined in application code.

B The query syntax is invalid because DynamoDB requires double quotes around table names.

C DynamoDB requires a WHERE clause for all queries, so this query is incomplete.

D DynamoDB only supports queries on primary keys, so JOINs on foreign keys are disallowed.

💡 Hint

Think about how NoSQL databases handle relationships compared to relational databases.

DynamoDB does not support SQL JOINs. Data relationships must be handled by denormalizing data or joining in application logic.