Views for security and abstraction in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a SQL view?

A SQL view is a virtual table based on the result of a SQL query. It does not store data itself but shows data from one or more tables.

beginner

How do views help with security in databases?

Views restrict user access by showing only specific columns or rows, hiding sensitive data from users who don't have full table access.

intermediate

Explain abstraction in the context of SQL views.

Abstraction means hiding complex table structures or joins behind a simple view, so users can work with easy-to-understand data without knowing the details.

intermediate

Can you update data through a SQL view?

Some views are updatable, meaning you can insert, update, or delete data through them if they meet certain conditions, like referencing a single table without aggregates.

beginner

Write a simple SQL statement to create a view that shows only employee names and departments.

CREATE VIEW EmployeeDept AS SELECT name, department FROM Employees;

What does a SQL view store?

A The actual data from tables

B Indexes for faster queries

C Only the query definition, not data

D User permissions

A view stores only the SQL query definition, not the actual data.

How can views improve database security?

A By encrypting the data

B By speeding up queries

C By backing up data automatically

D By hiding sensitive columns or rows

Views can hide sensitive columns or rows, limiting what users see.

Which of these is a benefit of using views for abstraction?

A Users must write complex joins

B Users see simplified data structures

C Views increase storage space

D Views prevent all data updates

Views simplify data by hiding complex joins or calculations.

When is a view updatable?

A When it references a single table without aggregates

B When it uses aggregate functions

C When it includes multiple tables with joins

D When it contains subqueries

Views are updatable if they reference a single table and avoid aggregates or complex joins.

Which SQL keyword is used to create a view?

A CREATE VIEW

B CREATE TABLE

C CREATE INDEX

D CREATE PROCEDURE

CREATE VIEW is used to define a new view.

Describe how views can be used to protect sensitive data in a database.

Think about showing only what users need to see.

Explain the concept of abstraction with SQL views and why it is helpful for users.

Imagine making a complicated table look simple.

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