Why PostgreSQL over other databases - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

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

PostgreSQL

SELECT [1] FROM employees;

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 blank empty.

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

2fill in blank

medium

Complete the code to filter employees with salary greater than 50000.

PostgreSQL

SELECT * FROM employees WHERE salary [1] 50000;

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

A<=

B<

C=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using < or <= which select smaller or equal values.

Using = which selects only equal values.

The symbol > means 'greater than' in SQL conditions.

3fill in blank

hard

Fix the error in the code to count employees in each department.

PostgreSQL

SELECT department, COUNT([1]) FROM employees GROUP BY department;

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

Asalary

B*

Cdepartment

Demployee_id

Attempts:

3 left

💡 Hint

Common Mistakes

Counting a specific column which may have NULLs and cause wrong counts.

Using a column that is not unique or relevant.

Using COUNT(*) counts all rows in each group, which is standard for counting employees.

4fill in blank

hard

Fill both blanks to create a table named products with id as primary key.

PostgreSQL

CREATE TABLE products (id [1] PRIMARY KEY, name [2] NOT NULL);

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

ASERIAL

BVARCHAR(100)

CINTEGER

DTEXT

Attempts:

3 left

💡 Hint

Common Mistakes

Using TEXT for id which does not auto-increment.

Using INTEGER for name which is not text.

SERIAL creates an auto-incrementing integer for id. VARCHAR(100) defines a text column with max 100 characters for name.

5fill in blank

hard

Fill all three blanks to update the salary of employee with id 10 to 60000.

PostgreSQL

UPDATE employees SET salary = [1] WHERE id [2] [3];

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

A50000

B60000

C10

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong salary value.

Using wrong comparison operator.

Swapping id and salary values.

We set salary to 60000, and use = to match employee with id 10.

Practice

1. Why is PostgreSQL often chosen over other databases for many projects?

easy

A. Because it only works with small datasets

B. Because it has no community support

C. Because it requires expensive licenses

D. Because it is free, reliable, and supports many features

Solution

1. Step 1: Understand PostgreSQL's cost and reliability

   PostgreSQL is open-source and free, making it accessible and reliable for many users.

2. Step 2: Recognize its feature set and community

   It supports many advanced features and has a strong community, unlike options that are costly or limited.

3. Final Answer:

   Because it is free, reliable, and supports many features -> Option D

4. Quick Check:

   PostgreSQL = free + reliable + feature-rich [OK]

Hint: Remember: free + reliable + features = PostgreSQL strength [OK]

Common Mistakes:

• Thinking PostgreSQL is expensive
• Assuming it only works for small data
• Ignoring community support importance

2. Which of the following is the correct way to install PostgreSQL on a Linux system using the command line?

easy

A. install postgresql sudo

B. sudo apt-get install postgresql

C. postgresql install sudo apt-get

D. sudo postgresql install apt-get

Solution

1. Step 1: Identify the correct package manager command

   On Debian-based Linux, the command to install packages is 'sudo apt-get install [package]'.

2. Step 2: Check command syntax order

   The correct syntax places 'sudo apt-get install' before the package name 'postgresql'.

3. Final Answer:

   sudo apt-get install postgresql -> Option B

4. Quick Check:

   Correct install command syntax = sudo apt-get install postgresql [OK]

Hint: Remember: sudo apt-get install + package name [OK]

Common Mistakes:

• Mixing command order
• Omitting sudo
• Using wrong keywords

3. What will be the output of this SQL query in PostgreSQL?

SELECT version();

medium

A. The current PostgreSQL version string

B. An error about missing table

C. Empty result set

D. List of all databases

Solution

1. Step 1: Understand the function used

   The function version() returns a string describing the PostgreSQL version and build info.

2. Step 2: Predict the query output

   Since no table is referenced, no error occurs; the output is a single row with version info.

3. Final Answer:

   The current PostgreSQL version string -> Option A

4. Quick Check:

   SELECT version() returns version info [OK]

Hint: version() returns PostgreSQL version info string [OK]

Common Mistakes:

• Expecting table data output
• Thinking it lists databases
• Assuming it causes error

4. You wrote this query in PostgreSQL:

SELECT * FROM users WHERE id = 'abc';

But it returns no rows even though you expect some. What is the likely problem?

medium

A. The query syntax is invalid

B. The table users does not exist

C. The id column is numeric, but 'abc' is a string

D. PostgreSQL does not support WHERE clause

Solution

1. Step 1: Check data type mismatch

   If id is numeric but compared to a non-numeric string 'abc', no rows match.

2. Step 2: Confirm query syntax and table existence

   The syntax is valid and table likely exists; the mismatch causes no results.

3. Final Answer:

   The id column is numeric, but 'abc' is a string -> Option C

4. Quick Check:

   Data type mismatch = no rows [OK]

Hint: Check data types in WHERE clause values [OK]

Common Mistakes:

• Assuming syntax error
• Ignoring data type mismatch
• Thinking table is missing

5. Which PostgreSQL feature allows you to extend the database with custom functions and data types, making it more flexible than many other databases?

hard

A. Extensions and custom procedural languages

B. Fixed schema with no extensions

C. Limited to basic SQL only

D. No support for user-defined functions

Solution

1. Step 1: Identify PostgreSQL extensibility features

   PostgreSQL supports extensions and custom procedural languages to add new functions and types.

2. Step 2: Compare with other databases

   Many other databases have fixed schemas or limited extensibility, making PostgreSQL more flexible.

3. Final Answer:

   Extensions and custom procedural languages -> Option A

4. Quick Check:

   PostgreSQL extensibility = extensions + custom functions [OK]

Hint: Remember: PostgreSQL supports extensions and custom functions [OK]

Common Mistakes:

• Thinking PostgreSQL has fixed schema
• Assuming no user-defined functions
• Confusing with limited SQL-only databases