NoSQL database types (document, key-value, column, graph) in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the NoSQL database type from its description

Which NoSQL database type stores data as flexible, self-describing JSON-like documents allowing nested structures and varied fields per record?

A Document store

B Key-value store

C Column store

D Graph database

💡 Hint

Think about databases that store data in JSON or BSON format.

Document stores save data as documents, often JSON-like, which can have nested fields and flexible schemas.

🧠 Conceptual

intermediate

Match the NoSQL type to its main use case

Which NoSQL database type is best suited for storing and querying relationships between entities, such as social networks or recommendation systems?

A Column store

B Key-value store

C Document store

D Graph database

💡 Hint

Think about databases that model data as nodes and edges.

Graph databases specialize in storing entities and their relationships, making them ideal for social networks.

❓ query_result

advanced

Output of a key-value store retrieval

Given a key-value store with pairs: {"user1": "Alice", "user2": "Bob", "user3": "Carol"}, what is the output of retrieving the value for key "user2"?

HLD

GET user2

A "Alice"

B "Bob"

C null

D "user2"

💡 Hint

Key-value stores return the value for the given key.

The key "user2" maps to the value "Bob" in the store.

🧠 Conceptual

advanced

Identify the correct column-family query syntax

Which option shows a valid CQL (Cassandra Query Language) statement to select all columns from the "users" table where "userid" equals 123?

A SELECT * FROM users WHERE userid = 123;

B SELECT ALL FROM users WHERE userid == 123;

C GET * FROM users WHERE userid = 123;

D SELECT * FROM users WHERE userid = '123';

💡 Hint

CQL syntax is similar to SQL but uses single equals for conditions.

Option A uses correct CQL syntax with single equals and semicolon.

🔍 Analysis

expert

Find the error in a graph database query

Given this Cypher query to find friends of 'Alice': MATCH (a:Person {name: 'Alice'})-[:FRIEND]->(friend) RETURN friend.name, which option describes the error if the query returns no results despite data existing?

A The node label should be lowercase :person instead of :Person

B The property name should be friend.names instead of friend.name

C The relationship type should be lowercase :friend instead of :FRIEND

D The query is missing a WHERE clause to filter by name

💡 Hint

Relationship types in Cypher are case-sensitive.

Cypher relationship types are case-sensitive; if data uses :friend but query uses :FRIEND, no matches occur.