Views for security and abstraction in SQL

Introduction

Views help keep data safe and simple. They show only what you want others to see.

You want to hide sensitive columns like passwords from users.

You want to show only certain rows of a big table to some users.

You want to make complex data easier to understand by showing a simple table.

You want to reuse a common query without writing it again.

You want to control what parts of data different teams can access.

Syntax

SQL

CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

A view is like a saved query that looks like a table.

You can select from a view just like a normal table.

Examples

This view shows only employee IDs and names, hiding other details.

SQL

CREATE VIEW EmployeeNames AS
SELECT EmployeeID, Name
FROM Employees;

This view shows only customers who are active.

SQL

CREATE VIEW ActiveCustomers AS
SELECT * FROM Customers
WHERE Status = 'Active';

This view summarizes total sales per product.

SQL

CREATE VIEW SalesSummary AS
SELECT ProductID, SUM(Quantity) AS TotalSold
FROM Sales
GROUP BY ProductID;

Sample Program

This example creates an Employees table, adds data, then creates a view showing only IT department employees with their IDs and names. Finally, it selects all from the view.

SQL

CREATE TABLE Employees (
  EmployeeID INT,
  Name VARCHAR(50),
  Salary DECIMAL(10,2),
  Department VARCHAR(50)
);

INSERT INTO Employees VALUES
(1, 'Alice', 70000, 'HR'),
(2, 'Bob', 80000, 'IT'),
(3, 'Charlie', 75000, 'IT');

CREATE VIEW IT_Employees AS
SELECT EmployeeID, Name
FROM Employees
WHERE Department = 'IT';

SELECT * FROM IT_Employees;

Important Notes

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

Using views can improve security by limiting data exposure.

Views can simplify complex queries for users who don't need all details.

Summary

Views act like windows to your data, showing only what you want.

They help keep sensitive data safe and make data easier to use.

You create views with a SELECT query saved as a virtual table.

Practice

1. What is the main purpose of using a VIEW in SQL?

easy

A. To permanently store data in the database

B. To provide a simplified and secure way to access specific data

C. To create a backup of the database

D. To speed up the database server hardware

Solution

1. Step 1: Understand what a VIEW is

   A VIEW is a virtual table created by a SELECT query that shows data without storing it separately.

2. Step 2: Identify the purpose of a VIEW

   It helps users see only the data they need, hiding sensitive details and simplifying complex queries.

3. Final Answer:

   To provide a simplified and secure way to access specific data -> Option B

4. Quick Check:

   VIEW = Simplify + Secure access [OK]

Hint: Views show selected data safely without storing it separately [OK]

Common Mistakes:

• Thinking views store data permanently
• Confusing views with backups
• Believing views improve hardware speed

2. Which of the following is the correct syntax to create a view named EmployeeView showing only EmployeeID and Name from Employees table?

easy

A. CREATE VIEW EmployeeView AS SELECT EmployeeID, Name FROM Employees;

B. MAKE VIEW EmployeeView SELECT EmployeeID, Name FROM Employees;

C. CREATE TABLE EmployeeView AS SELECT EmployeeID, Name FROM Employees;

D. VIEW CREATE EmployeeView SELECT EmployeeID, Name FROM Employees;

Solution

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

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

2. Step 2: Match the syntax with options

   CREATE VIEW EmployeeView AS SELECT EmployeeID, Name FROM Employees; matches the correct syntax exactly.

3. Final Answer:

   CREATE VIEW EmployeeView AS SELECT EmployeeID, Name FROM Employees; -> Option A

4. Quick Check:

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

Hint: Use CREATE VIEW ... AS SELECT ... to define views [OK]

Common Mistakes:

• Using MAKE VIEW instead of CREATE VIEW
• Confusing CREATE VIEW with CREATE TABLE
• Incorrect keyword order

3. Given the table Employees with columns EmployeeID, Name, Salary, and a view EmployeeView defined as:

CREATE VIEW EmployeeView AS SELECT EmployeeID, Name FROM Employees;

What will the query SELECT * FROM EmployeeView; return?

medium

A. Only Salary column

B. All columns: EmployeeID, Name, Salary

C. Only EmployeeID and Name columns

D. Syntax error because Salary is missing

Solution

1. Step 1: Understand the view definition

   The view selects only EmployeeID and Name columns from Employees.

2. Step 2: Determine what SELECT * from the view returns

   It returns only the columns defined in the view, which are EmployeeID and Name.

3. Final Answer:

   Only EmployeeID and Name columns -> Option C

4. Quick Check:

   View columns = Selected columns only [OK]

Hint: View shows only columns defined in its SELECT query [OK]

Common Mistakes:

• Expecting all original table columns
• Thinking missing columns cause syntax errors
• Confusing view columns with table columns

4. Consider this incorrect SQL statement to create a view:

CREATE VIEW SalesView SELECT OrderID, Amount FROM Sales;

What is the error and how to fix it?

medium

A. Incorrect view name; fix by renaming view

B. Missing FROM keyword; fix by adding FROM before Sales

C. SELECT statement is not allowed in views

D. Missing AS keyword; fix by adding AS after view name

Solution

1. Step 1: Identify the syntax error in CREATE VIEW

   The correct syntax requires AS keyword after the view name.

2. Step 2: Correct the statement

   Add AS after SalesView: CREATE VIEW SalesView AS SELECT OrderID, Amount FROM Sales;

3. Final Answer:

   Missing AS keyword; fix by adding AS after view name -> Option D

4. Quick Check:

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

Hint: Always use AS after view name in CREATE VIEW [OK]

Common Mistakes:

• Omitting AS keyword
• Misplacing FROM keyword
• Thinking SELECT is disallowed in views

5. You want to create a view PublicEmployeeData that hides the Salary column from the Employees table but allows users to see EmployeeID, Name, and Department. Which SQL statement correctly creates this view and ensures security by restricting access to sensitive data?

hard

A. CREATE VIEW PublicEmployeeData AS SELECT EmployeeID, Name, Department FROM Employees;

B. CREATE VIEW PublicEmployeeData AS SELECT * FROM Employees WHERE Salary IS NULL;

C. CREATE VIEW PublicEmployeeData AS SELECT EmployeeID, Name, Department, Salary FROM Employees;

D. CREATE VIEW PublicEmployeeData AS SELECT EmployeeID, Name FROM Employees;

Solution

1. Step 1: Identify columns to include and exclude

   We want EmployeeID, Name, Department but NOT Salary to protect sensitive data.

2. Step 2: Choose the correct SELECT statement for the view

   CREATE VIEW PublicEmployeeData AS SELECT EmployeeID, Name, Department FROM Employees; selects only the allowed columns, hiding Salary effectively.

3. Final Answer:

   CREATE VIEW PublicEmployeeData AS SELECT EmployeeID, Name, Department FROM Employees; -> Option A

4. Quick Check:

   View excludes Salary to secure sensitive data [OK]

Hint: Select only non-sensitive columns in view to protect data [OK]

Common Mistakes:

• Including Salary column accidentally
• Using WHERE Salary IS NULL which filters rows, not columns
• Selecting too few columns missing Department