First Normal Form (1NF) in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main rule of First Normal Form (1NF) in databases?

1NF requires that each column in a table contains only atomic (indivisible) values, and each record is unique with no repeating groups or arrays.

beginner

Why should a table not have repeating groups or arrays in 1NF?

Repeating groups or arrays make data hard to query and update. 1NF avoids this by ensuring each field holds only one value, making data simpler and consistent.

beginner

Which of these violates 1NF?<br>

StudentID | Courses
1         | Math, Science
2         | English

This violates 1NF because the 'Courses' column contains multiple values (Math, Science) in one field. Each field should have only one value.

intermediate

How can you fix a table that violates 1NF due to multiple values in one column?

You can create a separate row for each value or use a related table to store multiple values, so each field holds only one atomic value.

beginner

What does it mean for a value to be atomic in the context of 1NF?

Atomic means the value cannot be divided further. For example, a single phone number is atomic, but a list of phone numbers in one field is not.

Which of the following is a violation of First Normal Form (1NF)?

A A column contains multiple phone numbers separated by commas

B Each row has a unique ID

C Each column contains only one value

D No duplicate rows exist

1NF requires each column to have atomic values. Multiple phone numbers in one field violate this.

What does 1NF ensure about the structure of a database table?

A Tables have indexes

B Foreign keys are used properly

C Data is encrypted

D No repeating groups and atomic column values

1NF focuses on eliminating repeating groups and ensuring atomic values in columns.

How can you correct a table that stores multiple values in one column to meet 1NF?

A Add more columns with the same values

B Split the values into separate rows or related tables

C Use a comma-separated string in the same column

D Ignore it, 1NF does not care

Splitting values into separate rows or tables ensures atomicity and meets 1NF.

Which of these is an atomic value suitable for 1NF?

A A single email address

B A list of hobbies separated by commas

C Multiple phone numbers in one field

D An array of tags

An atomic value is indivisible, like a single email address.

What problem does 1NF help to avoid?

A Lack of user permissions

B Slow network connections

C Data redundancy and complex queries due to multi-valued fields

D Incorrect data types

1NF avoids multi-valued fields that cause redundancy and make queries complex.

Explain in your own words what First Normal Form (1NF) means and why it is important.

Think about how data should be stored in each column.

Describe a real-life example where a table violates 1NF and how you would fix it.

Imagine a list of phone numbers stored in one cell.