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

Recall & Review

beginner

What is the First Normal Form (1NF) in database normalization?

1NF means that a table has only atomic (indivisible) values in each column and each record is unique. There should be no repeating groups or arrays.

beginner

Why is it important for a table to be in 1NF?

Being in 1NF helps avoid duplicate data and makes it easier to search, update, and maintain the database.

intermediate

Which of the following violates 1NF?

StudentID | Courses
1         | Math, Science
2         | English

This violates 1NF because the 'Courses' column contains multiple values (Math, Science) instead of atomic values.

intermediate

How can you convert a table that violates 1NF into 1NF?

Split the multi-valued columns into separate rows so each cell contains only one value. For example, list each course in a separate row with the student ID.

beginner

Does 1NF require a primary key in the table?

Yes, 1NF requires that each row is unique, which means the table must have a primary key or a unique identifier.

What does 1NF ensure in a database table?

A Data is encrypted

B Each column contains atomic values only

C Table has no primary key

D Table has multiple repeating groups

1NF requires that each column contains atomic (indivisible) values only.

Which of these violates 1NF?

A A table with multiple phone numbers in one cell

B A table with unique rows

C A table with a primary key

D A table with single values in each cell

Multiple values in one cell violate 1NF because values must be atomic.

How can you fix a table that violates 1NF due to multi-valued columns?

A Remove the table

B Add more columns with multiple values

C Split multi-valued columns into separate rows

D Ignore the problem

Splitting multi-valued columns into separate rows ensures atomicity and fixes 1NF violation.

Does 1NF allow repeating groups in a table?

A No, never

B Yes, always

C Only if primary key exists

D Only for numeric data

1NF does not allow repeating groups; each field must contain only one value.

What is a key requirement for a table to be in 1NF?

A Data must be encrypted

B Columns can have multiple values

C No primary key needed

D Each row must be unique

Each row must be unique, usually ensured by a primary key, for 1NF compliance.

Explain what First Normal Form (1NF) means in database design and why it is important.

Think about how data should be stored in simple, indivisible pieces.

Describe how you would convert a table that has multiple values in one column into 1NF.

Consider splitting data to avoid lists inside a single cell.

Practice

1. What does First Normal Form (1NF) primarily ensure in a database table?

easy

A. Tables have multiple primary keys

B. Tables have no foreign keys

C. Each cell contains only one atomic value

D. Data is encrypted for security

Solution

1. Step 1: Understand the definition of 1NF

   1NF requires that each column in a table holds atomic (indivisible) values, meaning no multiple values or lists in a single cell.

2. Step 2: Compare options with 1NF definition

   Only Each cell contains only one atomic value matches this requirement. Other options relate to different concepts like keys or security.

3. Final Answer:

   Each cell contains only one atomic value -> Option C

4. Quick Check:

   1NF = atomic values only [OK]

Hint: 1NF means no multiple values in one cell [OK]

Common Mistakes:

• Confusing 1NF with encryption or keys
• Thinking 1NF allows multiple values in a cell
• Mixing 1NF with higher normal forms

2. Which of the following table structures violates First Normal Form (1NF)?

easy

A. A table with a column storing multiple phone numbers separated by commas

B. A table where each column contains only single values

C. A table with unique primary keys for each row

D. A table with no repeating rows

Solution

1. Step 1: Identify the 1NF violation

   1NF forbids multiple values in a single cell. Storing multiple phone numbers separated by commas means one cell holds multiple values.

2. Step 2: Check other options

   Options B, C, and D follow 1NF rules because they have atomic values and unique rows.

3. Final Answer:

   A table with a column storing multiple phone numbers separated by commas -> Option A

4. Quick Check:

   Multiple values in one cell violate 1NF [OK]

Hint: Look for columns with multiple values in one cell [OK]

Common Mistakes:

• Assuming commas separate values correctly in 1NF
• Confusing unique rows with atomic values
• Ignoring multi-valued columns

3. Consider this table data:
StudentID | Courses
1 | Math, Science
2 | English
3 | Math, English
Which statement is true about this table regarding 1NF?

medium

A. The table violates 1NF because the Courses column has multiple values

B. The table is in 1NF because Courses are listed as text

C. The table is in 1NF because each row has a unique StudentID

D. The table violates 1NF because StudentID is not unique

Solution

1. Step 1: Analyze the Courses column

   The Courses column contains multiple values separated by commas in some rows, which means cells are not atomic.

2. Step 2: Check uniqueness and 1NF rules

   Although StudentID is unique, 1NF requires atomic values in each cell. Multiple courses in one cell violate 1NF.

3. Final Answer:

   The table violates 1NF because the Courses column has multiple values -> Option A

4. Quick Check:

   Multiple values in one cell break 1NF [OK]

Hint: Check if any cell holds multiple values separated by commas [OK]

Common Mistakes:

• Thinking unique keys alone satisfy 1NF
• Ignoring multi-valued columns
• Assuming text format means atomic values

4. You have a table with columns: OrderID, ProductIDs where ProductIDs stores multiple product IDs separated by semicolons. How would you fix this to comply with 1NF?

medium

A. Remove the ProductIDs column entirely

B. Keep the table as is because semicolons separate values

C. Combine all ProductIDs into one string without separators

D. Split the table so each row has one ProductID per OrderID

Solution

1. Step 1: Identify the 1NF violation

   Storing multiple product IDs in one cell violates 1NF because values are not atomic.

2. Step 2: Apply 1NF correction

   Splitting the table so each row has one ProductID per OrderID ensures atomic values and removes repeating groups.

3. Final Answer:

   Split the table so each row has one ProductID per OrderID -> Option D

4. Quick Check:

   One value per cell fixes 1NF violation [OK]

Hint: Make each cell hold only one value by splitting rows [OK]

Common Mistakes:

• Thinking separators alone satisfy 1NF
• Removing columns instead of fixing data structure
• Combining values into one string without atomicity

5. A table stores employee skills as follows:
EmpID | Skills
101 | Java, Python
102 | Python
103 | Java, SQL, Python
How can you transform this table into 1NF compliant form?

hard

A. Keep skills as comma-separated values in one cell

B. Create a new row for each skill per EmpID

C. Remove the Skills column and store skills elsewhere

D. Combine all skills into a single string without commas

Solution

1. Step 1: Identify multi-valued attribute

   The Skills column contains multiple skills separated by commas, violating 1NF.

2. Step 2: Normalize by creating multiple rows

   To comply with 1NF, create a separate row for each skill linked to the same EmpID, making each cell atomic.

3. Final Answer:

   Create a new row for each skill per EmpID -> Option B

4. Quick Check:

   One skill per row ensures 1NF compliance [OK]

Hint: Turn multi-valued cells into multiple rows [OK]

Common Mistakes:

• Leaving multi-valued cells unchanged
• Removing data instead of restructuring
• Combining values without atomicity