Why views matter in PostgreSQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple view named 'active_users' that shows users with status 'active'.

PostgreSQL

CREATE VIEW active_users AS SELECT * FROM users WHERE status = '[1]';

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

Aactive

Binactive

Cpending

Ddeleted

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a status other than 'active' will show wrong users.

Leaving the status blank will cause a syntax error.

The view filters users with status 'active'. So the correct value is 'active'.

2fill in blank

medium

Complete the code to select all columns from the view 'active_users'.

PostgreSQL

SELECT [1] FROM active_users;

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

Aid

Bname

C*

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting a single column when all columns are needed.

Using an invalid column name.

Using '*' selects all columns from the view.

3fill in blank

hard

Fix the error in the view definition by completing the missing keyword.

PostgreSQL

CREATE [1] active_users AS SELECT * FROM users WHERE status = 'active';

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

AFUNCTION

BINDEX

CTABLE

DVIEW

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'TABLE' instead of 'VIEW' causes syntax errors.

Using 'INDEX' or 'FUNCTION' is incorrect for views.

The keyword 'VIEW' is required to create a view in PostgreSQL.

4fill in blank

hard

Fill both blanks to create a view that shows orders with amount greater than 100.

PostgreSQL

CREATE [1] high_value_orders AS SELECT * FROM orders WHERE amount [2] 100;

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

AVIEW

B>

C<

DTABLE

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'TABLE' instead of 'VIEW' causes errors.

Using '<' instead of '>' filters wrong rows.

We create a VIEW named 'high_value_orders' and filter orders where amount is greater than 100 using '>'.

5fill in blank

hard

Fill all three blanks to create a view that shows product names and prices where price is less than 50.

PostgreSQL

CREATE [1] affordable_products AS SELECT [2], price FROM products WHERE price [3] 50;

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

AVIEW

Bname

C<

DTABLE

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'TABLE' instead of 'VIEW' causes errors.

Selecting wrong column instead of 'name'.

Using '>' instead of '<' filters wrong products.

We create a VIEW named 'affordable_products', select 'name' and 'price' columns, and filter where price is less than 50 using '<'.

Practice

1. What is the main purpose of using a VIEW in PostgreSQL?

easy

A. To save a complex query as a reusable object

B. To permanently store data separately from tables

C. To speed up data insertion into tables

D. To delete rows from multiple tables at once

Solution

1. Step 1: Understand what a VIEW is

   A VIEW in PostgreSQL is a saved SQL query that acts like a virtual table.

2. Step 2: Identify the main use of a VIEW

   It simplifies complex queries by letting you reuse them without rewriting.

3. Final Answer:

   To save a complex query as a reusable object -> Option A

4. Quick Check:

   Views simplify queries = A [OK]

Hint: Views store queries, not data, for easy reuse [OK]

Common Mistakes:

• Thinking views store data separately
• Confusing views with tables
• Assuming views speed up inserts

2. Which of the following is the correct syntax to create a view named active_users showing users with status = 'active'?

easy

A. CREATE VIEW active_users AS SELECT * FROM users WHERE status = 'active';

B. CREATE active_users VIEW AS SELECT * FROM users WHERE status = 'active';

C. VIEW CREATE active_users AS SELECT * FROM users WHERE status = 'active';

D. CREATE VIEW active_users SELECT * FROM users WHERE status = 'active';

Solution

1. Step 1: Recall the correct CREATE VIEW syntax

   The syntax is: CREATE VIEW view_name AS SELECT ...

2. Step 2: Match the syntax with options

   CREATE VIEW active_users AS SELECT * FROM users WHERE status = 'active'; matches the correct syntax exactly.

3. Final Answer:

   CREATE VIEW active_users AS SELECT * FROM users WHERE status = 'active'; -> Option A

4. Quick Check:

   CREATE VIEW ... AS SELECT ... = B [OK]

Hint: Remember: CREATE VIEW name AS SELECT ... [OK]

Common Mistakes:

• Swapping keywords CREATE and VIEW
• Omitting AS keyword
• Incorrect keyword order

3. Given the table orders with columns id, customer, and amount, what will this view return?

CREATE VIEW big_orders AS SELECT customer, amount FROM orders WHERE amount > 100;

Then running:

SELECT * FROM big_orders;

medium

A. Syntax error because id is missing in view

B. All orders showing id, customer, and amount

C. All orders with amount greater than 100 showing customer and amount

D. Only orders with amount less than or equal to 100

Solution

1. Step 1: Understand the view definition

   The view selects customer and amount from orders where amount is greater than 100.

2. Step 2: Predict the SELECT * from the view

   It returns only customer and amount columns for orders with amount > 100.

3. Final Answer:

   All orders with amount greater than 100 showing customer and amount -> Option C

4. Quick Check:

   View filters amount > 100 and selects customer, amount = D [OK]

Hint: View columns = selected columns, filtered by WHERE [OK]

Common Mistakes:

• Expecting all columns to appear
• Confusing filter condition direction
• Thinking missing columns cause errors

4. You created a view with:

CREATE VIEW recent_sales AS SELECT * FROM sales WHERE sale_date > CURRENT_DATE - INTERVAL '7 days';

But running SELECT * FROM recent_sales; returns an error. What is the likely cause?

medium

A. CURRENT_DATE cannot be used in a view definition

B. The view definition is correct; error is elsewhere

C. The view needs to be refreshed manually to update data

D. The INTERVAL syntax is invalid in the view definition

Solution

1. Step 1: Check if INTERVAL and CURRENT_DATE are valid

   Both INTERVAL and CURRENT_DATE are valid in PostgreSQL and can be used in views.

2. Step 2: Understand view behavior

   Views are virtual and always reflect current data; no manual refresh needed.

3. Final Answer:

   The view definition is correct; error is elsewhere -> Option B

4. Quick Check:

   Valid syntax means error is not in view code = A [OK]

Hint: Check error source; valid syntax means problem is outside view [OK]

Common Mistakes:

• Assuming CURRENT_DATE is disallowed in views
• Thinking views store data needing refresh
• Blaming INTERVAL syntax without checking error message

5. You want to restrict users to see only active employees' names and departments without exposing salaries. Which approach using views is best?

hard

A. Create a view selecting name, department, and salary for all employees

B. Create a view selecting all columns but filter status = 'active'

C. Create a view selecting only salary and status columns

D. Create a view selecting only name and department from employees where status = 'active'

Solution

1. Step 1: Identify data to expose

   Only active employees' names and departments should be visible, no salaries.

2. Step 2: Choose view that filters and limits columns

   Create a view selecting only name and department from employees where status = 'active' selects only needed columns and filters active status, protecting salary data.

3. Final Answer:

   Create a view selecting only name and department from employees where status = 'active' -> Option D

4. Quick Check:

   View limits columns and filters rows = C [OK]

Hint: Select only needed columns and filter rows in view [OK]

Common Mistakes:

• Including salary column exposing sensitive data
• Not filtering active status
• Selecting all columns unnecessarily