Updatable views in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple updatable view showing employee names and salaries.

PostgreSQL

CREATE VIEW employee_salaries AS SELECT name, [1] FROM employees;

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

Aage

Bdepartment

Csalary

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a column unrelated to salary like age or department.

Selecting the employee ID instead of salary.

The view should select the salary column to show employee salaries.

2fill in blank

medium

Complete the code to update the salary of an employee through the view.

PostgreSQL

UPDATE employee_salaries SET [1] = 60000 WHERE name = 'Alice';

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

Aname

Bsalary

Cdepartment

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to update the name or department instead of salary.

Using the employee ID which is not updatable in this view.

To update the salary, set the salary column in the view.

3fill in blank

hard

Fix the error in the view definition to make it updatable by adding the clause that enforces the WHERE condition.

PostgreSQL

CREATE VIEW employee_info AS SELECT name, salary FROM employees WHERE department = 'Sales' [1];

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

AWITH CHECK OPTION

BWITH LOCAL CHECK OPTION

CWITH CASCADED CHECK OPTION

DWITH PRIMARY KEY

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'WITH PRIMARY KEY' which is not valid syntax here.

Omitting the check option, causing update errors.

The WITH CHECK OPTION ensures updates through the view meet the view's conditions, making it updatable.

4fill in blank

hard

Fill both blanks to create an updatable view that includes the employee ID and enforces updates only for the HR department.

PostgreSQL

CREATE VIEW hr_employees AS SELECT [1], name, salary FROM employees WHERE department = [2] WITH CHECK OPTION;

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

Aid

B'HR'

C'Sales'

Dsalary

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong department name in the filter.

Omitting the primary key column which is needed for updates.

The employee id is needed for updates, and the filter must be for the 'HR' department.

5fill in blank

hard

Fill all three blanks to create an updatable view that shows employee ID, name, and salary, and only allows updates for employees with salary greater than 50000.

PostgreSQL

CREATE VIEW high_earners AS SELECT [1], [2], [3] FROM employees WHERE salary > 50000 WITH CHECK OPTION;

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

Aid

Bname

Csalary

Ddepartment

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving out the primary key column 'id'.

Including columns not needed or missing salary.

The view must include id, name, and salary columns to be updatable and show the correct data.

Practice

1. What is an updatable view in PostgreSQL?

easy

A. A function that returns a set of rows

B. A view that only shows data but cannot be changed

C. A table that stores data permanently

D. A view that allows you to change data in the underlying table through it

Solution

1. Step 1: Understand the definition of a view

   A view is a saved query that shows data from one or more tables.

2. Step 2: Identify what makes a view updatable

   An updatable view lets you change data in the underlying table by modifying the view.

3. Final Answer:

   A view that allows you to change data in the underlying table through it -> Option D

4. Quick Check:

   Updatable view = change data through view [OK]

Hint: Updatable views let you edit data through the view [OK]

Common Mistakes:

• Confusing views with tables
• Thinking all views are read-only
• Believing views store data themselves

2. Which of the following is the correct syntax to create a simple updatable view on a single table employees showing id and name columns?

easy

A. CREATE VIEW emp_view AS SELECT id, name FROM employees;

B. CREATE VIEW emp_view AS UPDATE employees SET name = 'John';

C. CREATE TABLE emp_view AS SELECT id, name FROM employees;

D. CREATE FUNCTION emp_view() RETURNS TABLE(id INT, name TEXT) AS $$ SELECT id, name FROM employees; $$ LANGUAGE SQL;

Solution

1. Step 1: Recall the syntax to create a view

   The syntax is CREATE VIEW view_name AS SELECT columns FROM table;

2. Step 2: Check each option

   CREATE VIEW emp_view AS SELECT id, name FROM employees; matches the correct syntax for a simple view. The other options are incorrect because they use UPDATE, CREATE TABLE, or FUNCTION instead of CREATE VIEW.

3. Final Answer:

   CREATE VIEW emp_view AS SELECT id, name FROM employees; -> Option A

4. Quick Check:

   CREATE VIEW uses SELECT query [OK]

Hint: CREATE VIEW uses SELECT, not UPDATE or TABLE [OK]

Common Mistakes:

• Using UPDATE instead of SELECT in CREATE VIEW
• Confusing CREATE VIEW with CREATE TABLE
• Trying to create a function instead of a view

3. Given the table products(id, name, price) and the view CREATE VIEW cheap_products AS SELECT id, name FROM products WHERE price < 100; What happens if you try to update the name of a product through cheap_products view?

medium

A. The update changes only the view but not the underlying table

B. The update fails because the view filters rows with a WHERE clause

C. The update succeeds and changes the product name in the products table

D. The update causes a syntax error

Solution

1. Step 1: Understand updatable views with WHERE clause

   Views that select from a single base table with a restricting WHERE clause are updatable in PostgreSQL.

2. Step 2: Check the effect of updating through filtered view

   Updating the name of a product visible in the view (price < 100) will successfully update the underlying products table.

3. Final Answer:

   The update succeeds and changes the product name in the products table -> Option C

4. Quick Check:

   Single-table views with WHERE are updatable [OK]

Hint: Single-table views with WHERE filters are updatable [OK]

Common Mistakes:

• Thinking WHERE clause prevents updates
• Thinking update affects only the view
• Expecting syntax error instead of runtime error

4. You created a view with this SQL:
CREATE VIEW emp_dept AS SELECT e.id, e.name, d.name AS dept_name FROM employees e JOIN departments d ON e.dept_id = d.id;
When you try to update emp_dept to change an employee's name, you get an error. What is the main reason?

medium

A. The view joins multiple tables, so it is not automatically updatable

B. The view does not include the employee's ID column

C. The view uses aliases for columns, causing syntax errors

D. The view is missing a WHERE clause

Solution

1. Step 1: Analyze the view definition

   The view joins two tables: employees and departments.

2. Step 2: Understand updatable view rules for joins

   Views that join multiple tables are not automatically updatable in PostgreSQL because the system cannot decide how to update multiple tables from one view.

3. Final Answer:

   The view joins multiple tables, so it is not automatically updatable -> Option A

4. Quick Check:

   Joined views are not updatable by default [OK]

Hint: Views with joins are not updatable automatically [OK]

Common Mistakes:

• Thinking missing ID causes update failure
• Blaming column aliases for errors
• Assuming WHERE clause is required for updates

5. You want to make a complex view updatable that joins orders and customers tables. Which PostgreSQL feature should you use to allow updates through this view?

hard

A. Use a materialized view instead of a regular view

B. Create INSTEAD OF triggers on the view to handle updates

C. Add a WHERE clause to the view to filter rows

D. Create a function that returns the joined data

Solution

1. Step 1: Understand limitations of updatable views with joins

   Views joining multiple tables are not automatically updatable in PostgreSQL.

2. Step 2: Use INSTEAD OF triggers to enable updates

   INSTEAD OF triggers let you define custom update logic on complex views, making them updatable.

3. Final Answer:

   Create INSTEAD OF triggers on the view to handle updates -> Option B

4. Quick Check:

   INSTEAD OF triggers enable updates on complex views [OK]

Hint: Use INSTEAD OF triggers for complex view updates [OK]

Common Mistakes:

• Thinking WHERE clause makes view updatable
• Confusing materialized views with updatable views
• Believing functions replace update triggers