Why views are needed in SQL - See It in Action

Understanding Why Views Are Needed in SQL

📖 Scenario: You are working as a database assistant for a small company. The company has a table that stores employee information, including sensitive data like salaries. You want to create a way for managers to see employee names and departments without exposing sensitive salary information.

🎯 Goal: Build a simple SQL view that shows only employee names and departments, hiding sensitive salary data. This will help managers access only the information they need.

📋 What You'll Learn

Create a table called employees with columns id, name, department, and salary.

Insert at least three employees with exact values.

Create a view called employee_overview that shows only name and department.

Use the view to select all employee names and departments.

💡 Why This Matters

🌍 Real World

Companies often need to share parts of their data with different teams without exposing everything. Views let them do this safely and easily.

💼 Career

Database administrators and developers use views to control data access and simplify complex queries for users.

1

Create the employees table and insert data

Create a table called employees with columns id (integer), name (text), department (text), and salary (integer). Then insert these exact rows: (1, 'Alice', 'HR', 50000), (2, 'Bob', 'IT', 60000), (3, 'Charlie', 'Finance', 55000).

SQL

-- Create the employees table and insert data
-- Your code here

Hint

Use CREATE TABLE to define the table and INSERT INTO to add rows.

2

Create a view to show only names and departments

Create a view called employee_overview that selects only the name and department columns from the employees table.

SQL

CREATE TABLE employees (
  id INTEGER,
  name TEXT,
  department TEXT,
  salary INTEGER
);

INSERT INTO employees (id, name, department, salary) VALUES
  (1, 'Alice', 'HR', 50000),
  (2, 'Bob', 'IT', 60000),
  (3, 'Charlie', 'Finance', 55000);

-- Create the employee_overview view here
-- Your code here

Hint

Use CREATE VIEW view_name AS SELECT ... to create the view.

3

Query the view to see employee names and departments

Write a SQL query to select all columns from the employee_overview view.

SQL

CREATE TABLE employees (
  id INTEGER,
  name TEXT,
  department TEXT,
  salary INTEGER
);

INSERT INTO employees (id, name, department, salary) VALUES
  (1, 'Alice', 'HR', 50000),
  (2, 'Bob', 'IT', 60000),
  (3, 'Charlie', 'Finance', 55000);

CREATE VIEW employee_overview AS
SELECT name, department FROM employees;

-- Select all from employee_overview
-- Your code here

Hint

Use SELECT * FROM view_name to query the view.

4

Explain why views are useful

Add a comment explaining why creating the employee_overview view is helpful for the company.

SQL

CREATE TABLE employees (
  id INTEGER,
  name TEXT,
  department TEXT,
  salary INTEGER
);

INSERT INTO employees (id, name, department, salary) VALUES
  (1, 'Alice', 'HR', 50000),
  (2, 'Bob', 'IT', 60000),
  (3, 'Charlie', 'Finance', 55000);

CREATE VIEW employee_overview AS
SELECT name, department FROM employees;

SELECT * FROM employee_overview;

-- Add a comment explaining why views are useful
-- Your code here

Hint

Write a comment starting with -- explaining the benefit of views.

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