Types of databases (relational, NoSQL, object-oriented) in DBMS Theory - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the database type from description

Which type of database stores data in tables with rows and columns and uses SQL for queries?

A Relational database

B NoSQL database

C Object-oriented database

D Graph database

💡 Hint

Think about databases that organize data in rows and columns.

Relational databases organize data in tables with rows and columns and use SQL to query data.

❓ query_result

intermediate

Output of NoSQL document query

Given a NoSQL document database with a collection of user documents, what is the output of this query?

db.users.find({"age": {"$gt": 30}})

Assuming the collection has three users aged 25, 35, and 40.

A Returns users aged 35 and 40

B Returns users aged 25 only

C Returns no users

D Returns users aged 25, 35, and 40

💡 Hint

The query filters users older than 30.

The query finds users with age greater than 30, so it returns users aged 35 and 40.

📋 Factual

advanced

Identify the correct object-oriented database query syntax

Which of the following is a valid way to query objects in an object-oriented database?

A db.objects.find({type: 'Car'})

B objects->filter(type == 'Car')

C SELECT * FROM objects WHERE objectType = 'Car'

D GET /objects?filter=type:Car

💡 Hint

Object-oriented databases often use method calls on objects.

Option B uses a method call style typical for object-oriented databases to filter objects.

❓ optimization

advanced

Best database type for hierarchical data

You need to store and query hierarchical data like organizational charts efficiently. Which database type is best suited?

A Relational database with JOINs

B NoSQL document database

C Object-oriented database

D Graph database

💡 Hint

Think about databases designed for relationships and connections.

Graph databases are optimized for hierarchical and relationship data, making queries efficient.

🔍 Analysis

expert

Why does this NoSQL query fail?

Consider this NoSQL query:

db.products.find({price: {$lt: '100'}})

It returns no results even though products with price less than 100 exist as numbers. Why?

A The $lt operator is invalid in NoSQL queries

B The collection name 'products' is incorrect

C The query uses a string '100' instead of a number 100

D No products have a price field

💡 Hint

Check the data types used in the query condition.

The query compares price to a string '100' but prices are stored as numbers, so no match occurs.

Practice

1. Which type of database stores data in tables and uses SQL for queries?

easy

A. Object-oriented database

B. NoSQL database

C. Graph database

D. Relational database

Solution

1. Step 1: Understand database types

   Relational databases organize data in tables with rows and columns.

2. Step 2: Identify query language

   They use SQL (Structured Query Language) to manage and query data.

3. Final Answer:

   Relational database -> Option D

4. Quick Check:

   Tables + SQL = Relational database [OK]

Hint: Tables and SQL mean relational database [OK]

Common Mistakes:

• Confusing NoSQL with relational because both store data
• Thinking object-oriented databases use SQL
• Assuming graph databases are relational

2. Which of the following is the correct way to describe a NoSQL database?

easy

A. Stores flexible data like documents or key-value pairs

B. Stores data only in tables with fixed schema

C. Stores data as objects matching programming languages

D. Uses only SQL for data queries

Solution

1. Step 1: Recall NoSQL database features

   NoSQL databases store data flexibly, often as documents or key-value pairs.

2. Step 2: Eliminate incorrect options

   They do not require fixed schemas or only tables, and do not rely solely on SQL.

3. Final Answer:

   Stores flexible data like documents or key-value pairs -> Option A

4. Quick Check:

   No fixed schema + flexible data = NoSQL [OK]

Hint: Flexible data storage means NoSQL [OK]

Common Mistakes:

• Thinking NoSQL uses only tables
• Confusing object-oriented with NoSQL
• Assuming NoSQL requires SQL queries

3. Given the following description, which database type fits best?
Data is stored as objects with properties and methods, similar to programming languages.

medium

A. Relational database

B. NoSQL database

C. Object-oriented database

D. Hierarchical database

Solution

1. Step 1: Analyze data storage style

   The data is stored as objects with properties and methods, matching programming language objects.

2. Step 2: Match to database type

   Object-oriented databases store data as objects, unlike relational or NoSQL databases.

3. Final Answer:

   Object-oriented database -> Option C

4. Quick Check:

   Objects with methods = Object-oriented database [OK]

Hint: Objects with methods mean object-oriented DB [OK]

Common Mistakes:

• Confusing object-oriented with NoSQL
• Thinking relational databases store objects
• Assuming hierarchical is object-oriented

4. Identify the error in this statement:
NoSQL databases always use SQL queries to retrieve data.

medium

A. No error, statement is correct

B. NoSQL databases do not use SQL queries

C. NoSQL databases only store data in tables

D. NoSQL databases are a type of relational database

Solution

1. Step 1: Understand NoSQL query methods

   NoSQL databases typically use query methods other than SQL, like JSON queries or key-value lookups.

2. Step 2: Identify the error

   The statement wrongly claims NoSQL always uses SQL, which is false.

3. Final Answer:

   NoSQL databases do not use SQL queries -> Option B

4. Quick Check:

   NoSQL ≠ SQL queries [OK]

Hint: NoSQL means no SQL queries [OK]

Common Mistakes:

• Believing NoSQL uses SQL
• Confusing NoSQL with relational
• Thinking NoSQL stores only tables

5. A company wants to store user profiles with flexible fields that can change often, and also wants to store some complex objects with methods for processing. Which combination of databases should they use?

hard

A. A NoSQL database for flexible data and an object-oriented database for complex objects

B. Only a relational database

C. Only a NoSQL database

D. Only an object-oriented database

Solution

1. Step 1: Analyze data needs

   Flexible fields suggest NoSQL for schema flexibility; complex objects with methods suggest object-oriented database.

2. Step 2: Choose suitable combination

   Using both NoSQL and object-oriented databases fits the requirements best.

3. Final Answer:

   A NoSQL database for flexible data and an object-oriented database for complex objects -> Option A

4. Quick Check:

   Flexible + complex objects = NoSQL + object-oriented [OK]

Hint: Use NoSQL for flexible, object-oriented for complex objects [OK]

Common Mistakes:

• Choosing only relational database ignoring flexibility
• Using only NoSQL and ignoring object methods
• Assuming object-oriented alone handles flexible fields