Why views are needed in SQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple view that shows all employees.

SQL

CREATE VIEW employee_view AS SELECT [1] FROM employees;

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

Aname

Bid

Csalary

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using a specific column name instead of selecting all columns.

Leaving the SELECT statement empty.

The * selects all columns from the employees table to include in the view.

2fill in blank

medium

Complete the code to select only the name and salary columns from the view.

SQL

SELECT [1] FROM employee_view;

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

Aname, salary

Bid, department

Csalary, id

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting all columns (*) instead of specific ones.

Mixing up column names.

To get only the name and salary columns, list them separated by a comma.

3fill in blank

hard

Fix the error in the view creation by completing the code correctly.

SQL

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

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

Aview_employee

Bemployee_view

Cemployees_view

Demployee

Attempts:

3 left

💡 Hint

Common Mistakes

Using table names instead of view names.

Using ambiguous or unclear names.

The view name should be employee_view to follow naming conventions and clarity.

4fill in blank

hard

Fill both blanks to create a view that shows only employees with salary greater than 50000.

SQL

CREATE VIEW [1] AS SELECT name, salary FROM employees WHERE salary [2] 50000;

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

Ahigh_salary_employees

B>

C<

Demployee_salaries

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator.

Choosing unclear view names.

The view name high_salary_employees describes the content, and the operator > filters salaries greater than 50000.

5fill in blank

hard

Fill all three blanks to create a view that shows employee names in uppercase and their departments, only for departments with more than 10 employees.

SQL

CREATE VIEW [1] AS SELECT [2] AS name_upper, department FROM employees WHERE department IN (SELECT department FROM employees GROUP BY department HAVING COUNT(*) [3] 10);

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

Adept_large_employees

BUPPER(name)

C>

DLOWER(name)

Attempts:

3 left

💡 Hint

Common Mistakes

Using LOWER instead of UPPER for name conversion.

Using wrong comparison operator in HAVING clause.

Choosing unclear or unrelated view names.

The view name dept_large_employees fits the purpose. UPPER(name) converts names to uppercase. The operator > filters departments with more than 10 employees.

Practice

1. Why do we use views in a database?
SELECT * FROM view_name; What is the main purpose of this?

easy

A. To speed up the database server hardware

B. To permanently store data physically in the database

C. To delete data from multiple tables at once

D. To simplify complex queries by showing only needed data

Solution

1. Step 1: Understand what a view does

   A view is a saved query that shows data in a simpler way without storing data separately.

2. Step 2: Identify the main purpose of views

   Views help users see only the data they need, hiding complexity and sensitive info.

3. Final Answer:

   To simplify complex queries by showing only needed data -> Option D

4. Quick Check:

   Views simplify data = C [OK]

Hint: Views show simpler data without storing it [OK]

Common Mistakes:

• Thinking views store data physically
• Confusing views with database hardware
• Believing views delete data

2. Which of the following is the correct syntax to create a view named EmployeeView that shows only name and salary from Employees table?

easy

A. CREATE VIEW EmployeeView AS SELECT name, salary FROM Employees;

B. CREATE TABLE EmployeeView AS SELECT name, salary FROM Employees;

C. INSERT VIEW EmployeeView SELECT name, salary FROM Employees;

D. VIEW CREATE EmployeeView SELECT name, salary FROM Employees;

Solution

1. Step 1: Recall the syntax for creating a view

   The correct syntax starts with CREATE VIEW, then the view name, followed by AS and the SELECT query.

2. Step 2: Match the options with correct syntax

   CREATE VIEW EmployeeView AS SELECT name, salary FROM Employees; matches the correct syntax exactly; others use wrong keywords or order.

3. Final Answer:

   CREATE VIEW EmployeeView AS SELECT name, salary FROM Employees; -> Option A

4. Quick Check:

   CREATE VIEW + AS + SELECT = B [OK]

Hint: Use CREATE VIEW ... AS SELECT ... [OK]

Common Mistakes:

• Using CREATE TABLE instead of CREATE VIEW
• Wrong keyword order like INSERT VIEW
• Omitting AS keyword

3. Given the table Sales with columns product, region, and amount, and the view:
CREATE VIEW RegionalSales AS SELECT region, SUM(amount) AS total FROM Sales GROUP BY region;
What will the query SELECT * FROM RegionalSales WHERE total > 1000; return?

medium

A. All rows from Sales table without filtering

B. Rows showing regions where total sales amount is more than 1000

C. Syntax error because views cannot use GROUP BY

D. Empty result because total is not a column in Sales

Solution

1. Step 1: Understand the view definition

   The view groups sales by region and sums amounts, creating a total per region.

2. Step 2: Analyze the query on the view

   The query filters regions where total sales exceed 1000, so it returns those regions and totals.

3. Final Answer:

   Rows showing regions where total sales amount is more than 1000 -> Option B

4. Quick Check:

   View groups and filters totals > 1000 = A [OK]

Hint: Views can use GROUP BY and filters on aggregated columns [OK]

Common Mistakes:

• Thinking views cannot use GROUP BY
• Confusing view columns with base table columns
• Assuming syntax error due to alias

4. You tried to create a view with:
CREATE VIEW MyView AS SELECT id, password FROM Users;
But you want to hide the password column for security. What is the best fix?

medium

A. Remove password from the SELECT list in the view

B. Rename the view to hide the password

C. Add WHERE password IS NOT NULL clause

D. Use DELETE to remove password column from Users table

Solution

1. Step 1: Identify the problem with the view

   The view currently shows the password column, which exposes sensitive data.

2. Step 2: Fix the view to hide sensitive data

   Removing the password column from the SELECT statement prevents it from appearing in the view.

3. Final Answer:

   Remove password from the SELECT list in the view -> Option A

4. Quick Check:

   Exclude sensitive columns from view SELECT = D [OK]

Hint: Exclude sensitive columns in view SELECT to hide them [OK]

Common Mistakes:

• Trying to rename view to hide data
• Using WHERE clause to filter columns
• Deleting columns from base table instead of view

5. You want to create a view that shows only active customers with their total orders, but the Orders table has millions of rows. Which approach best uses views to improve performance and security?

hard

A. Create a view that deletes inactive customers from the database

B. Create a view selecting all customers and orders without filters

C. Create a view filtering active customers and pre-aggregating order totals

D. Create a view that stores all orders physically to speed queries

Solution

1. Step 1: Understand the goal for the view

   The view should show only active customers and their total orders to reduce data size and protect inactive data.

2. Step 2: Choose the best approach for performance and security

   Filtering and pre-aggregating in the view reduces data scanned and hides unnecessary info, improving speed and security.

3. Final Answer:

   Create a view filtering active customers and pre-aggregating order totals -> Option C

4. Quick Check:

   Filter and aggregate in view for speed and security = A [OK]

Hint: Filter and aggregate in views to improve speed and hide data [OK]

Common Mistakes:

• Selecting all data without filters
• Trying to delete data via views
• Misunderstanding views store data physically