Why databases over files in SQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all records from the users table.

SQL

SELECT [1] FROM users;

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

AALL

BALL_COLUMNS

CEVERY

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using ALL or EVERY instead of * to select all columns.

The asterisk (*) selects all columns from the table.

2fill in blank

medium

Complete the code to find records where age is greater than 30.

SQL

SELECT * FROM employees WHERE age [1] 30;

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

A>

B=

C<

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '=' instead of '>' for greater than comparison.

The '>' operator means 'greater than' in SQL.

3fill in blank

hard

Fix the error in the SQL query to count the number of orders.

SQL

SELECT COUNT([1]) FROM orders;

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

A*

Border_id

Call

Dorders

Attempts:

3 left

💡 Hint

Common Mistakes

Using COUNT(orders) or COUNT(all) which are invalid.

Using COUNT(*) counts all rows in the table.

4fill in blank

hard

Fill both blanks to select names and ages of employees older than 25.

SQL

SELECT [1], [2] FROM employees WHERE age > 25;

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

Aname

Bage

Csalary

Ddepartment

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting salary or department instead of name and age.

We select 'name' and 'age' columns to see employees' names and ages.

5fill in blank

hard

Fill all three blanks to create a dictionary of product names and prices where price is above 100.

SQL

SELECT [1], [2] FROM products WHERE [3] > 100;

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

Aproduct_name

Bprice

Dquantity

Attempts:

3 left

💡 Hint

Common Mistakes

Using quantity instead of price in the WHERE clause.

Select product_name and price columns where price is greater than 100.

Practice

1. Why do we prefer databases over simple files for storing data?

easy

A. Databases cannot store large amounts of data.

B. Files are faster to search than databases.

C. Databases allow multiple users to access and update data safely at the same time.

D. Files automatically protect data better than databases.

Solution

1. Step 1: Understand data access needs

   Multiple users often need to read and write data simultaneously in real life, like in banks or stores.

2. Step 2: Compare files and databases

   Simple files do not handle multiple users well and can cause data loss or errors. Databases manage this safely.

3. Final Answer:

   Databases allow multiple users to access and update data safely at the same time. -> Option C

4. Quick Check:

   Multiple safe access = Databases [OK]

Hint: Databases handle many users safely, files do not [OK]

Common Mistakes:

• Thinking files are faster to search than databases
• Believing files protect data better automatically
• Assuming databases cannot store large data

2. Which of the following is the correct reason why databases are better than files?

easy

A. Databases support concurrent access with data integrity.

B. Databases do not allow data updates once saved.

C. Files automatically create backups.

D. Files can handle complex queries easily.

Solution

1. Step 1: Review database features

   Databases allow many users to access and update data at the same time without corrupting it.

2. Step 2: Check file limitations

   Files do not manage concurrent access well and do not ensure data integrity during updates.

3. Final Answer:

   Databases support concurrent access with data integrity. -> Option A

4. Quick Check:

   Concurrent safe access = Databases [OK]

Hint: Databases keep data safe when many users update [OK]

Common Mistakes:

• Believing databases prevent any data updates
• Thinking files create backups automatically
• Assuming files handle complex queries easily

3. Consider a system where multiple users try to update a customer record stored in a simple file simultaneously. What is the most likely outcome?

medium

A. All updates will be saved correctly without any data loss.

B. The system will convert the file into a database automatically.

C. The file will automatically lock and queue updates safely.

D. Some updates may overwrite others causing data loss or corruption.

Solution

1. Step 1: Understand file behavior with multiple writes

   Simple files do not manage simultaneous writes well, so one update can overwrite another.

2. Step 2: Compare with database behavior

   Databases use locks and transactions to prevent such data loss, but files lack this feature.

3. Final Answer:

   Some updates may overwrite others causing data loss or corruption. -> Option D

4. Quick Check:

   Simultaneous file writes = Data loss risk [OK]

Hint: Files lack safe multi-user update controls [OK]

Common Mistakes:

• Assuming files lock automatically
• Believing all updates save correctly
• Thinking files convert to databases automatically

4. You have a file-based system where users report data inconsistencies after simultaneous updates. What is the best fix?

medium

A. Switch to a database system that supports transactions and concurrency control.

B. Increase the file size limit to avoid data loss.

C. Allow only one user to access the file at a time manually.

D. Use a faster computer to reduce update time.

Solution

1. Step 1: Identify the cause of inconsistencies

   Simultaneous updates on files cause conflicts and data corruption due to lack of concurrency control.

2. Step 2: Choose a solution that handles concurrency

   Databases provide transactions and locking to manage multiple users safely, fixing inconsistencies.

3. Final Answer:

   Switch to a database system that supports transactions and concurrency control. -> Option A

4. Quick Check:

   Concurrency fix = Use database [OK]

Hint: Use databases for safe multi-user updates [OK]

Common Mistakes:

• Thinking increasing file size helps concurrency
• Believing manual single-user access is practical
• Assuming faster computers fix data conflicts

5. A company stores customer orders in files but faces issues with data loss and slow searches. How can switching to a database solve these problems?

hard

A. Databases delete old data automatically to save space.

B. Databases organize data in tables with indexes, speeding up searches and preventing data loss with backups and transactions.

C. Databases store data as plain text files, so no change occurs.

D. Databases require manual file locking to avoid conflicts.

Solution

1. Step 1: Identify file system problems

   Files lack indexing, making searches slow, and have no built-in backup or transaction support, risking data loss.

2. Step 2: Understand database advantages

   Databases store data in tables with indexes for fast search and use transactions and backups to protect data.

3. Final Answer:

   Databases organize data in tables with indexes, speeding up searches and preventing data loss with backups and transactions. -> Option B

4. Quick Check:

   Tables + indexes + transactions = Faster, safer data [OK]

Hint: Databases speed search and protect data with transactions [OK]

Common Mistakes:

• Thinking databases store data as plain text files
• Believing databases delete old data automatically
• Assuming manual locking is needed in databases