Querying from views in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all columns from the view named 'employee_view'.

MySQL

SELECT * FROM [1];

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

Aemployee

Bemployees

Cemployee_view

Dview_employee

Attempts:

3 left

💡 Hint

Common Mistakes

Using the base table name instead of the view name.

Misspelling the view name.

The correct way to query all data from a view is to use its exact name after FROM. Here, the view is named 'employee_view'.

2fill in blank

medium

Complete the code to select the 'name' column from the view 'department_view'.

MySQL

SELECT [1] FROM department_view;

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

A*

Bdepartment

Cdept_name

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting the whole view with '*' when only one column is needed.

Using a wrong column name.

To select a specific column, use its exact column name. Here, 'name' is the correct column in the view.

3fill in blank

hard

Fix the error in the query to select all from the view 'sales_view'.

MySQL

SELECT * FROM [1];

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

Asales_view

Bsalesview

Csales view

Dsales-view

Attempts:

3 left

💡 Hint

Common Mistakes

Using spaces or dashes in the view name.

Omitting underscores.

The view name must be exact and without spaces or special characters. 'sales_view' is correct.

4fill in blank

hard

Fill both blanks to select the 'employee_id' and 'salary' columns from the view 'payroll_view'.

MySQL

SELECT [1], [2] FROM payroll_view;

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

Aemployee_id

Bsalary

Cemp_id

Dwage

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect or abbreviated column names.

Mixing column names from other tables.

The correct column names in the view are 'employee_id' and 'salary'.

5fill in blank

hard

Fill all three blanks to select 'product_name', 'price', and 'stock' columns from the view 'inventory_view'.

MySQL

SELECT [1], [2], [3] FROM inventory_view;

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

Aproduct_name

Bprice

Cstock

Dquantity

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong column names or synonyms.

Forgetting commas between column names.

The columns in the view are 'product_name', 'price', and 'stock'. Use these exact names to query.

Practice

1. What is a view in MySQL?

easy

A. A virtual table based on a stored query

B. A physical table storing data permanently

C. A backup of a database

D. A user account with special permissions

Solution

1. Step 1: Understand the definition of a view

   A view is not a physical table but a saved query that acts like a table.

2. Step 2: Differentiate from other options

   Options A, B, and C describe physical tables, backups, or users, which are not views.

3. Final Answer:

   A virtual table based on a stored query -> Option A

4. Quick Check:

   View = virtual table [OK]

Hint: Remember: Views are saved queries, not real tables [OK]

Common Mistakes:

• Thinking views store data physically
• Confusing views with backups
• Assuming views are user accounts

2. Which of the following is the correct syntax to select all columns from a view named employee_view?

easy

A. SELECT ALL FROM employee_view;

B. SELECT * FROM VIEW employee_view;

C. SELECT * FROM employee_view;

D. GET * FROM employee_view;

Solution

1. Step 1: Recall standard SELECT syntax for views

   Views are queried like tables using SELECT * FROM view_name;

2. Step 2: Check each option's syntax

   SELECT * FROM employee_view; uses correct syntax. Options B, C, and D use invalid keywords or order.

3. Final Answer:

   SELECT * FROM employee_view; -> Option C

4. Quick Check:

   SELECT * FROM view_name; is correct [OK]

Hint: Query views like tables using SELECT * FROM view_name [OK]

Common Mistakes:

• Using VIEW keyword in SELECT statement
• Replacing SELECT with GET
• Using SELECT ALL instead of SELECT *

3. Given a view sales_view defined as SELECT product_id, SUM(quantity) AS total_qty FROM sales GROUP BY product_id, what will the query SELECT * FROM sales_view WHERE total_qty > 100; return?

medium

A. All products with total quantity sold greater than 100

B. All sales records with quantity greater than 100

C. Syntax error because WHERE cannot be used on views

D. Empty result because total_qty is not a column

Solution

1. Step 1: Understand the view definition

   The view groups sales by product_id and sums quantity as total_qty.

2. Step 2: Analyze the query on the view

   The query filters rows where total_qty > 100, so it returns products with total sales over 100.

3. Final Answer:

   All products with total quantity sold greater than 100 -> Option A

4. Quick Check:

   Filtering on view columns works normally [OK]

Hint: Filter views like tables using WHERE on view columns [OK]

Common Mistakes:

• Thinking WHERE can't be used on views
• Confusing total_qty with original quantity column
• Assuming syntax error due to aggregation

4. You have a view customer_view defined as SELECT id, name, email FROM customers; but running SELECT phone FROM customer_view; gives an error. What is the problem?

medium

A. Views cannot be queried for single columns

B. The column phone does not exist in the view

C. You must use SELECT * to query views

D. The view is corrupted and needs to be recreated

Solution

1. Step 1: Check the view's defined columns

   The view only includes id, name, and email columns, no phone column.

2. Step 2: Understand the error cause

   Querying a column not in the view causes an error because it doesn't exist in the virtual table.

3. Final Answer:

   The column phone does not exist in the view -> Option B

4. Quick Check:

   Query columns must exist in view definition [OK]

Hint: Check view columns before selecting them [OK]

Common Mistakes:

• Assuming views allow any column selection
• Thinking views are corrupted if column missing
• Believing SELECT * is mandatory for views

5. You want to create a view active_users_view that shows only users with status = 'active' from the users table. Which query correctly creates this view?

hard

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

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

C. CREATE VIEW active_users_view AS SELECT * FROM users HAVING status = 'active';

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

Solution

1. Step 1: Recall correct CREATE VIEW syntax

   The syntax requires CREATE VIEW view_name AS SELECT ... WHERE ...

2. Step 2: Check each option's correctness

   CREATE VIEW active_users_view AS SELECT * FROM users WHERE status = 'active'; uses correct syntax with WHERE clause. CREATE VIEW active_users_view SELECT * FROM users WHERE status = 'active'; misses AS keyword. CREATE VIEW active_users_view AS SELECT * FROM users HAVING status = 'active'; wrongly uses HAVING without GROUP BY. CREATE VIEW active_users_view AS SELECT * FROM users WHERE status == 'active'; uses invalid '==' operator.

3. Final Answer:

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

4. Quick Check:

   CREATE VIEW ... AS SELECT ... WHERE ... is correct [OK]

Hint: Use WHERE, not HAVING, and '=' for conditions in views [OK]

Common Mistakes:

• Omitting AS keyword
• Using HAVING without GROUP BY
• Using '==' instead of '=' in conditions