When to use SQL vs NoSQL in HLD - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all columns from a table named 'users'.

HLD

SELECT [1] FROM users;

Drag options to blanks, or click blank then click option'

A*

BALL

CCOLUMNS

DEVERYTHING

Attempts:

3 left

💡 Hint

Common Mistakes

Using words like ALL or COLUMNS instead of *

In SQL, * means select all columns from the table.

2fill in blank

medium

Complete the code to insert a new record into the 'products' table with columns 'name' and 'price'.

HLD

INSERT INTO products (name, price) VALUES ([1]);

Drag options to blanks, or click blank then click option'

A'Book'

B'Book', 12.99

C12.99

D'Book', '12.99'

Attempts:

3 left

💡 Hint

Common Mistakes

Providing only one value or quoting numbers incorrectly

When inserting multiple values, separate them by commas inside the parentheses.

3fill in blank

hard

Fix the error in the SQL query to update the 'age' of a user with id 5.

HLD

UPDATE users SET age = [1] WHERE id = 5;

Drag options to blanks, or click blank then click option'

A30

Bage = 30

Cage + 1

D'30'

Attempts:

3 left

💡 Hint

Common Mistakes

Putting numbers in quotes or using assignment syntax incorrectly

Numbers in SQL should not be in quotes when updating numeric columns.

4fill in blank

hard

Fill both blanks to create a NoSQL document filter that finds users older than 25.

HLD

{ 'age': { [1]: [2] } }

Drag options to blanks, or click blank then click option'

A$gt

B25

C$lt

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using $lt (less than) or wrong field names

In NoSQL (like MongoDB), $gt means 'greater than'.

5fill in blank

hard

Fill all three blanks to create a SQL query that selects users with age greater than 30 and orders by name ascending.

HLD

SELECT [1] FROM users WHERE age [2] 30 ORDER BY [3] ASC;

Drag options to blanks, or click blank then click option'

A*

B>

Cname

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators or ordering by wrong column

Select all columns, filter age greater than 30, and order by name ascending.

Practice

1. Which type of database is best suited for data with a fixed schema and strong relationships between tables?

easy

A. Flat file storage

B. NoSQL database

C. SQL database

D. In-memory cache

Solution

1. Step 1: Understand data structure needs

   Data with fixed schema and strong relationships fits well with structured tables.

2. Step 2: Match database type to structure

   SQL databases use tables and enforce schema, ideal for such data.

3. Final Answer:

   SQL database -> Option C

4. Quick Check:

   Structured data = SQL database [OK]

Hint: Fixed schema and relations? Choose SQL [OK]

Common Mistakes:

• Choosing NoSQL for strictly structured data
• Confusing flat files with databases
• Assuming in-memory cache stores persistent data

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

easy

A. They always use tables with fixed columns

B. They are designed for flexible, schema-less data storage

C. They require strict ACID transactions for all operations

D. They cannot handle large volumes of data

Solution

1. Step 1: Identify NoSQL characteristics

   NoSQL databases allow flexible, schema-less data models.

2. Step 2: Eliminate incorrect options

   They do not require fixed tables or strict ACID for all operations and can handle large data.

3. Final Answer:

   They are designed for flexible, schema-less data storage -> Option B

4. Quick Check:

   NoSQL = flexible schema [OK]

Hint: No fixed schema? NoSQL fits best [OK]

Common Mistakes:

• Thinking NoSQL always uses tables
• Assuming NoSQL can't scale
• Confusing ACID requirements with SQL only

3. Consider a social media app storing user posts that can have varying fields like text, images, or videos. Which database type will likely handle this data best?

medium

A. SQL database with fixed tables

B. CSV files for storage

C. Relational database with strict schema

D. NoSQL document database

Solution

1. Step 1: Analyze data variability

   User posts have varying fields, so schema flexibility is needed.

2. Step 2: Choose database type matching flexibility

   NoSQL document databases store flexible, nested data well.

3. Final Answer:

   NoSQL document database -> Option D

4. Quick Check:

   Variable fields = NoSQL document DB [OK]

Hint: Varying fields? Use NoSQL document DB [OK]

Common Mistakes:

• Choosing fixed-schema SQL for flexible data
• Using CSV which lacks query power
• Confusing relational DB with NoSQL

4. A developer tries to store rapidly changing sensor data with a fixed schema in a SQL database but faces performance issues. What is the likely cause and best fix?

medium

A. Fixed schema causes overhead; use a NoSQL database for flexibility

B. SQL databases are slow; switch to CSV files

C. Sensor data is small; use in-memory cache only

D. NoSQL databases cannot handle sensor data

Solution

1. Step 1: Identify problem with fixed schema and rapid changes

   Fixed schema in SQL causes overhead with frequent schema updates or inserts.

2. Step 2: Recommend flexible schema database

   NoSQL databases handle rapid, flexible data better, improving performance.

3. Final Answer:

   Fixed schema causes overhead; use a NoSQL database for flexibility -> Option A

4. Quick Check:

   Rapid changes + fixed schema = use NoSQL [OK]

Hint: Rapid, flexible data? NoSQL is better [OK]

Common Mistakes:

• Switching to CSV which lacks performance
• Assuming NoSQL can't handle sensor data
• Ignoring schema flexibility importance

5. You are designing a global e-commerce platform that needs to store user profiles, product catalogs, and handle millions of transactions per day. Which database strategy is best?

hard

A. Use SQL for transactions and NoSQL for product catalogs and user profiles

B. Use only SQL for all data to keep consistency

C. Use only NoSQL for all data to maximize flexibility

D. Use flat files for product catalogs and SQL for transactions

Solution

1. Step 1: Analyze data types and needs

   Transactions require strong consistency (SQL), catalogs and profiles need flexibility and scale (NoSQL).

2. Step 2: Combine database types for best fit

   Using SQL for transactions ensures ACID compliance; NoSQL handles flexible, large-scale data efficiently.

3. Final Answer:

   Use SQL for transactions and NoSQL for product catalogs and user profiles -> Option A

4. Quick Check:

   Mixed data needs = hybrid SQL + NoSQL [OK]

Hint: Mix SQL for transactions, NoSQL for flexible data [OK]

Common Mistakes:

• Using only SQL limits flexibility and scale
• Using only NoSQL risks transaction consistency
• Using flat files lacks query and scale support