View limitations in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

MySQL

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

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

Ainactive

Bdeleted

Cactive

Dpending

Attempts:

3 left

💡 Hint

Common Mistakes

Using status values other than 'active' will show wrong users.

Forgetting quotes around the status value causes syntax errors.

The view filters users with status 'active'. Using 'active' in the WHERE clause ensures only active users appear.

2fill in blank

medium

Complete the code to select from a view named 'sales_summary' only the rows where total_sales is greater than 1000.

MySQL

SELECT * FROM sales_summary WHERE total_sales [1] 1000;

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

A>

B<=

C=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '<=' will select smaller or equal values, not greater.

Using '=' will select only rows with exactly 1000 sales.

The condition 'total_sales > 1000' filters rows with sales greater than 1000.

3fill in blank

hard

Fix the error in the view creation by completing the code to avoid using a non-deterministic function in the view.

MySQL

CREATE VIEW current_time_view AS SELECT [1] AS now_time;

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

AUUID

BNOW

CRAND

DCURRENT_DATE

Attempts:

3 left

💡 Hint

Common Mistakes

Using NOW() or RAND() causes errors because they are non-deterministic.

Using UUID() is also non-deterministic and not allowed in views.

Views cannot use non-deterministic functions like NOW() or RAND(). CURRENT_DATE is deterministic for the day and allowed.

4fill in blank

hard

Fill both blanks to create a view that selects user_id and the count of orders, grouping by user_id.

MySQL

CREATE VIEW user_order_counts AS SELECT user_id, COUNT([1]) AS order_count FROM orders GROUP BY [2];

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

Aorder_id

Buser_id

Cstatus

Dtotal

Attempts:

3 left

💡 Hint

Common Mistakes

Counting user_id instead of order_id counts users, not orders.

Grouping by order_id groups by each order, not user.

Counting order_id counts orders per user. Grouping by user_id groups orders by each user.

5fill in blank

hard

Fill all three blanks to create a view that shows product names, total quantity sold, and only includes products with total quantity greater than 50.

MySQL

CREATE VIEW popular_products AS SELECT [1], SUM([2]) AS total_sold FROM sales GROUP BY [3] HAVING total_sold > 50;

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

Aproduct_name

Bquantity

Dprice

Attempts:

3 left

💡 Hint

Common Mistakes

Grouping by quantity or price instead of product_name causes wrong grouping.

Summing price instead of quantity does not count units sold.

The view selects product_name, sums quantity sold, groups by product_name, and filters to products with more than 50 sold.

Practice

1. Which of the following is true about MySQL views?

easy

A. Views always allow you to update data directly.

B. Views do not store data themselves; they show data from base tables.

C. Views can have indexes to speed up queries.

D. Views automatically create backup copies of data.

Solution

1. Step 1: Understand what a view is and check each option

   A view is a virtual table that shows data from one or more base tables but does not store data itself. Views do not store data themselves; they show data from base tables. matches the definition. Options A, C, and D are incorrect because views do not always allow updates, cannot have indexes, and do not store backup data.

2. Final Answer:

   Views do not store data themselves; they show data from base tables. -> Option B

3. Quick Check:

   Views are virtual tables = B [OK]

Hint: Remember: Views show data, they don't store it [OK]

Common Mistakes:

• Thinking views store data like tables
• Assuming views always allow updates
• Believing views can have indexes

2. Which of the following is the correct syntax to create a simple view in MySQL?

easy

A. CREATE VIEW AS SELECT * FROM table_name;

B. CREATE TABLE view_name AS SELECT * FROM table_name;

C. CREATE VIEW view_name FROM table_name;

D. CREATE VIEW view_name AS SELECT * FROM table_name;

Solution

1. Step 1: Recall the syntax for creating a view and compare options

   The correct syntax is: CREATE VIEW view_name AS SELECT ... CREATE VIEW view_name AS SELECT * FROM table_name; matches the correct syntax. CREATE TABLE view_name AS SELECT * FROM table_name; creates a table, not a view. CREATE VIEW view_name FROM table_name; has incorrect syntax.

2. Final Answer:

   CREATE VIEW view_name AS SELECT * FROM table_name; -> Option D

3. Quick Check:

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

Hint: Use 'CREATE VIEW name AS SELECT...' for views [OK]

Common Mistakes:

• Using CREATE TABLE instead of CREATE VIEW
• Omitting AS keyword
• Incorrect order of clauses

3. Given the view definition:
CREATE VIEW v_emp AS SELECT id, name FROM employees;
Which of the following queries will return the correct result?

medium

A. INSERT INTO v_emp (id, name) VALUES (6, 'Anna');

B. UPDATE v_emp SET name = 'John' WHERE id = 5;

C. SELECT * FROM v_emp WHERE id = 5;

D. DELETE FROM v_emp WHERE id = 5;

Solution

1. Step 1: Understand the view and its limitations, then analyze each query

   The view selects id and name from employees. Simple views on one table allow SELECT but may restrict UPDATE, INSERT, DELETE. SELECT * FROM v_emp WHERE id = 5; is a SELECT query and will work correctly. Options B, C, and D try to modify data through the view, which is often not allowed or restricted.

2. Final Answer:

   SELECT * FROM v_emp WHERE id = 5; -> Option C

3. Quick Check:

   Simple views allow SELECT only = A [OK]

Hint: Views usually allow SELECT, not data changes [OK]

Common Mistakes:

• Trying to update or insert through views without triggers
• Assuming all views are updatable
• Ignoring view restrictions on DELETE

4. You created a view with this statement:
CREATE VIEW v_sales AS SELECT order_id, customer_id, total FROM orders WHERE total > 100;
When you try to update the view with:
UPDATE v_sales SET total = 90 WHERE order_id = 10;
You get an error. What is the likely cause?

medium

A. The view contains a WHERE clause filtering rows, making it non-updatable.

B. You cannot update any view in MySQL.

C. The view does not include the primary key column.

D. The UPDATE syntax is incorrect for views.

Solution

1. Step 1: Identify view update restrictions and check the error cause

   Views with WHERE clauses or filtering conditions are often non-updatable because the database cannot guarantee consistent updates. The view contains a WHERE clause filtering rows, making it non-updatable. explains the error correctly. You cannot update any view in MySQL. is false because some views are updatable. The view does not include the primary key column. is incorrect because order_id is included. The UPDATE syntax is incorrect for views. is wrong as syntax is valid.

2. Final Answer:

   The view contains a WHERE clause filtering rows, making it non-updatable. -> Option A

3. Quick Check:

   WHERE clause in view blocks updates = A [OK]

Hint: Views with filters often block updates [OK]

Common Mistakes:

• Assuming all views are updatable
• Blaming syntax instead of view definition
• Ignoring WHERE clause effect on updates

5. You want to create a view that allows updating the salary column of employees but also shows the department name from a joined table. Which approach respects MySQL view limitations?

hard

A. Create a simple view on employees only, then update salary directly on employees table.

B. Create a view joining employees and departments, then update salary through the view.

C. Create a view with a WHERE clause filtering departments, then update salary through it.

D. Create a view with GROUP BY on departments and update salary through the view.

Solution

1. Step 1: Understand update restrictions on views with joins and choose the approach that allows updates

   Views that join multiple tables or use GROUP BY are generally non-updatable in MySQL. Create a simple view on employees only, then update salary directly on employees table. creates a simple view on one table, allowing updates on salary by updating the base table directly. Options A, B, and D involve joins, filters, or grouping, which block updates.

2. Final Answer:

   Create a simple view on employees only, then update salary directly on employees table. -> Option A

3. Quick Check:

   Simple single-table views allow updates = C [OK]

Hint: Update only through simple single-table views [OK]

Common Mistakes:

• Trying to update through joined or grouped views
• Assuming filters don't block updates
• Ignoring base table updates