CREATE VIEW syntax in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a view named 'active_users' that selects all columns from the 'users' table where 'status' is 'active'.

PostgreSQL

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

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

Aactive

B'active'

C"active"

DACTIVE

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put single quotes around string values.

Using double quotes which are for identifiers, not strings.

The value 'active' must be a string literal in SQL, so it needs single quotes.

2fill in blank

medium

Complete the code to create a view named 'recent_orders' that selects 'order_id' and 'order_date' from 'orders' where 'order_date' is after January 1, 2023.

PostgreSQL

CREATE VIEW recent_orders AS SELECT order_id, order_date FROM orders WHERE order_date > [1];

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

ADATE '2023-01-01'

B'2023-01-01'

C2023-01-01

D"2023-01-01"

Attempts:

3 left

💡 Hint

Common Mistakes

Using unquoted dates which cause syntax errors.

Using double quotes instead of single quotes for date strings.

In PostgreSQL, the DATE keyword before a string literal explicitly casts it as a date type, which is best practice here.

3fill in blank

hard

Fix the error in the code to create a view named 'customer_emails' selecting 'email' from 'customers'.

PostgreSQL

CREATE VIEW customer_emails [1] SELECT email FROM customers;

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

AON

BIS

CAS

DWITH

Attempts:

3 left

💡 Hint

Common Mistakes

Using IS or WITH instead of AS.

Omitting the keyword entirely.

The correct keyword to define the query for a view is AS.

4fill in blank

hard

Fill both blanks to create a view named 'top_products' selecting 'product_id' and 'sales' from 'products' where 'sales' is greater than 1000.

PostgreSQL

CREATE VIEW [1] AS SELECT product_id, sales FROM products WHERE sales [2] 1000;

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

Atop_products

B>

C<

Dbest_products

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong view name.

Using less than instead of greater than.

The view name should be 'top_products' and the condition is sales greater than 1000, so use >.

5fill in blank

hard

Fill all three blanks to create a view named 'employee_summary' selecting 'employee_id', 'department', and the count of projects as 'project_count' from 'employees' joined with 'projects' on 'employee_id', grouping by 'employee_id' and 'department'.

PostgreSQL

CREATE VIEW [1] AS SELECT employee_id, department, COUNT(project_id) AS [2] FROM employees JOIN projects ON employees.employee_id = projects.[3] GROUP BY employee_id, department;

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

Aemployee_summary

Bproject_count

Cemployee_id

Ddept_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong alias names.

Joining on the wrong column.

The view name is 'employee_summary', the alias for count is 'project_count', and the join is on 'employee_id'.

Practice

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

easy

A. To delete rows from a table

B. To save a SELECT query as a virtual table for easy reuse

C. To permanently store data in a new table

D. To create an index on a table column

Solution

1. Step 1: Understand what a view is

   A view is a virtual table that stores a SELECT query, not actual data.

2. Step 2: Identify the purpose of CREATE VIEW

   CREATE VIEW saves the SELECT query so you can reuse it easily without rewriting it.

3. Final Answer:

   To save a SELECT query as a virtual table for easy reuse -> Option B

4. Quick Check:

   CREATE VIEW = virtual table for queries [OK]

Hint: Views save SELECT queries as virtual tables [OK]

Common Mistakes:

• Thinking views store data permanently
• Confusing views with tables
• Using CREATE VIEW to delete data

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 view_name AS SELECT ... [OK]

Hint: Syntax is CREATE VIEW name AS SELECT ... [OK]

Common Mistakes:

• Swapping CREATE and VIEW keywords
• Omitting AS keyword
• Missing semicolon at the end

3. Given the table orders with columns order_id, customer_id, and amount, what will be the result of this view?

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

What rows will SELECT * FROM big_orders; return?

medium

A. No rows, syntax error in view

B. All orders with amount less than or equal to 100

C. All orders regardless of amount

D. All orders with amount greater than 100

Solution

1. Step 1: Analyze the SELECT query inside the view

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

2. Step 2: Understand what SELECT * FROM big_orders returns

   It returns all rows from the view, which are orders with amount > 100.

3. Final Answer:

   All orders with amount greater than 100 -> Option D

4. Quick Check:

   View filters orders with amount > 100 [OK]

Hint: View returns rows matching its SELECT query condition [OK]

Common Mistakes:

• Confusing greater than with less than
• Expecting all columns instead of selected ones
• Assuming syntax error without checking carefully

4. Identify the error in this CREATE VIEW statement:

CREATE VIEW recent_customers AS SELECT id, name FROM customers WHERE;

medium

A. Missing condition after WHERE keyword

B. Missing AS keyword before SELECT

C. View name cannot be recent_customers

D. SELECT must include all columns

Solution

1. Step 1: Check the syntax after WHERE

   The WHERE clause is incomplete; it must have a condition after WHERE.

2. Step 2: Verify other parts of the statement

   AS keyword is present, view name is valid, and SELECT columns are allowed to be partial.

3. Final Answer:

   Missing condition after WHERE keyword -> Option A

4. Quick Check:

   WHERE must have a condition [OK]

Hint: WHERE clause must have a condition [OK]

Common Mistakes:

• Leaving WHERE empty
• Forgetting AS keyword
• Thinking view names have restrictions

5. You want to create a view customer_orders that shows each customer's name and the total amount they spent. Which of these is the correct way to create this view assuming tables customers(id, name) and orders(customer_id, amount)?

hard

A. CREATE VIEW customer_orders AS SELECT c.name, o.amount FROM customers c, orders o WHERE c.id = o.customer_id;

B. CREATE VIEW customer_orders AS SELECT name, amount FROM customers JOIN orders ON id = customer_id;

C. CREATE VIEW customer_orders AS SELECT c.name, SUM(o.amount) FROM customers c JOIN orders o ON c.id = o.customer_id GROUP BY c.name;

D. CREATE VIEW customer_orders AS SELECT name, SUM(amount) FROM orders GROUP BY name;

Solution

1. Step 1: Understand the requirement

   We need each customer's name and total amount spent, so we must join customers and orders and sum amounts grouped by customer name.

2. Step 2: Check each option

   CREATE VIEW customer_orders AS SELECT c.name, SUM(o.amount) FROM customers c JOIN orders o ON c.id = o.customer_id GROUP BY c.name; correctly joins tables, sums amounts, and groups by customer name. Others miss grouping or join conditions.

3. Final Answer:

   CREATE VIEW customer_orders AS SELECT c.name, SUM(o.amount) FROM customers c JOIN orders o ON c.id = o.customer_id GROUP BY c.name; -> Option C

4. Quick Check:

   Join + SUM + GROUP BY = correct view [OK]

Hint: Use JOIN with GROUP BY and SUM for aggregation views [OK]

Common Mistakes:

• Missing GROUP BY when using SUM
• Not joining tables properly
• Selecting columns not in GROUP BY