Why server-side programming matters in PostgreSQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

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

PostgreSQL

SELECT [1] FROM users;

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

A*

Ball

Ceverything

Dcolumns

Attempts:

3 left

💡 Hint

Common Mistakes

Using words like 'all' or 'columns' instead of the symbol *.

Leaving the SELECT statement incomplete.

The asterisk (*) means select all columns from the table.

2fill in blank

medium

Complete the code to filter users with age greater than 18.

PostgreSQL

SELECT * FROM users WHERE age [1] 18;

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

A<

B<=

C=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' which means less than.

Using '=' which means equal to.

The '>' operator filters for ages greater than 18.

3fill in blank

hard

Fix the error in the query to count users by country.

PostgreSQL

SELECT country, COUNT([1]) FROM users GROUP BY country;

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

Auser_id

B*

Ccountry

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Counting a specific column that might have nulls, leading to wrong counts.

Using the grouping column inside COUNT which is not typical.

Using COUNT(*) counts all rows per country, which is correct here.

4fill in blank

hard

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

PostgreSQL

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

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

Aname

Bage

Ccountry

Demail

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting unrelated columns like 'country' or 'email'.

Selecting only one column instead of both.

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

5fill in blank

hard

Fill all three blanks to create a dictionary of user emails and their countries for users older than 30.

PostgreSQL

SELECT [1], [2] FROM users WHERE age [3] 30;

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

Aemail

Bcountry

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' for age comparison.

Selecting wrong columns like 'name' or 'age' instead of 'email' and 'country'.

Select 'email' and 'country' columns and filter users with age greater than 30.

Practice

1. Why is server-side programming important for managing data in a database?

easy

A. It centralizes data control and keeps data secure.

B. It runs only on the user's device.

C. It makes the website load slower.

D. It stores data only in the browser.

Solution

1. Step 1: Understand server-side role

   Server-side programming runs on a central server, not on user devices.

2. Step 2: Identify data management benefits

   This central control helps keep data safe and organized for all users.

3. Final Answer:

   It centralizes data control and keeps data secure. -> Option A

4. Quick Check:

   Server-side = central control and security [OK]

Hint: Server-side means central control of data [OK]

Common Mistakes:

• Thinking server-side runs on user devices
• Believing data is stored only in browsers
• Assuming server-side slows down websites

2. Which of the following is the correct way to write a simple SQL query in PostgreSQL to select all rows from a table named users?

easy

A. FETCH * users;

B. SELECT * FROM users;

C. GET ALL FROM users;

D. SELECT ALL users;

Solution

1. Step 1: Recall SQL SELECT syntax

   The correct syntax to get all rows is SELECT * FROM table_name;.

2. Step 2: Match syntax to options

   Only SELECT * FROM users; matches the correct SQL syntax for PostgreSQL.

3. Final Answer:

   SELECT * FROM users; -> Option B

4. Quick Check:

   SELECT * FROM table = correct query [OK]

Hint: SELECT * FROM table_name; is the standard query [OK]

Common Mistakes:

• Using GET or FETCH instead of SELECT
• Omitting FROM keyword
• Adding ALL incorrectly

3. Consider this PostgreSQL query run on a server:

INSERT INTO users (id, name) VALUES (1, 'Alice');
INSERT INTO users (id, name) VALUES (2, 'Bob');
SELECT * FROM users ORDER BY id;

What will be the output of the SELECT query?

medium

A. [{"id":1, "name":"Alice"}, {"id":2, "name":"Bob"}]

B. [{"name":"Alice"}, {"name":"Bob"}]

C. [{1, 'Alice'}, {2, 'Bob'}]

D. Syntax error

Solution

1. Step 1: Understand the INSERT commands

   Two rows are inserted with ids 1 and 2 and names Alice and Bob.

2. Step 2: Analyze the SELECT query

   The SELECT fetches all rows ordered by id, so rows appear in order 1 then 2.

3. Final Answer:

   [{"id":1, "name":"Alice"}, {"id":2, "name":"Bob"}] -> Option A

4. Quick Check:

   Inserted rows appear ordered by id [OK]

Hint: SELECT * ORDER BY id returns rows sorted by id [OK]

Common Mistakes:

• Ignoring ORDER BY and expecting random order
• Expecting only names without ids
• Thinking syntax error due to multiple inserts

4. You wrote this PostgreSQL query on the server:

SELECT name FROM users WHERE id = 'two';

But it returns no rows. What is the likely problem?

medium

A. The table users does not exist.

B. The query is missing a semicolon.

C. The SELECT keyword is misspelled.

D. The id column expects a number, but 'two' is a string.

Solution

1. Step 1: Check data type of id column

   Usually, id columns are numeric, so comparing to string 'two' fails to match.

2. Step 2: Understand why no rows return

   Since no id equals the string 'two', the query returns empty result.

3. Final Answer:

   The id column expects a number, but 'two' is a string. -> Option D

4. Quick Check:

   Data type mismatch causes no rows [OK]

Hint: Match data types in WHERE clause [OK]

Common Mistakes:

• Assuming table does not exist without checking
• Thinking missing semicolon causes no rows
• Ignoring data type mismatch

5. A web app uses server-side programming to handle user logins securely. Which of these is a key reason server-side code improves security compared to client-side only?

hard

A. Server-side code stores passwords in the browser cache.

B. Server-side code runs faster on the user's device.

C. Server-side code keeps passwords hidden and checks them safely on the server.

D. Server-side code allows users to see all database details.

Solution

1. Step 1: Understand server-side security role

   Server-side code processes sensitive data like passwords away from the user's device.

2. Step 2: Identify why this improves security

   Keeping passwords on the server prevents exposure and unauthorized access.

3. Final Answer:

   Server-side code keeps passwords hidden and checks them safely on the server. -> Option C

4. Quick Check:

   Server-side hides sensitive data from users [OK]

Hint: Passwords checked on server stay secure [OK]

Common Mistakes:

• Thinking server-side runs on user device
• Believing passwords are stored in browser cache
• Assuming users can see database details