First Normal Form (1NF) in SQL - Step-by-Step Execution

Concept Flow - First Normal Form (1NF)

Start with a Table

↓

Check for Atomicity

Yes / No?↓

Table in 1NF

↩[Split Multi- [Check for Repeating

Start with a table, check if each column has atomic (single) values and no repeating groups. If not, split or remove them until the table meets 1NF.

Execution Sample

SQL

CREATE TABLE Orders (
  OrderID INT,
  CustomerName VARCHAR(50),
  Items VARCHAR(100) -- comma separated
);

This table has a column 'Items' with multiple values in one field, which violates 1NF.

Execution Table

Step	Action	Table State	Reason
1	Initial table created	OrderID | CustomerName | Items 1 | Alice | 'Pen, Notebook' 2 | Bob | 'Pencil'	Items column has multiple values in one field (not atomic)
2	Check atomicity of 'Items'	Same as above	Items column violates 1NF because it stores multiple items in one field
3	Split 'Items' into separate rows	OrderID | CustomerName | Item 1 | Alice | Pen 1 | Alice | Notebook 2 | Bob | Pencil	Each field now atomic, no repeating groups
4	Table now in 1NF	Same as above	All columns have atomic values, no repeating groups

💡 Table meets 1NF after splitting multi-valued fields into atomic values in separate rows

Variable Tracker

Variable	Start	After Step 3	Final
Table Rows	2 rows with multi-valued Items	3 rows with atomic Item values	3 rows with atomic Item values
Items Column	'Pen, Notebook', 'Pencil'	'Pen', 'Notebook', 'Pencil'	'Pen', 'Notebook', 'Pencil'

Key Moments - 2 Insights

Why can't we keep multiple items in one 'Items' column field?

Because 1NF requires each column to hold atomic (single) values only. The execution_table row 2 shows that having 'Pen, Notebook' in one field violates this rule.

How do we fix a table that violates 1NF due to multi-valued fields?

We split the multi-valued field into multiple rows so each row has one atomic value, as shown in execution_table row 3.

Visual Quiz - 3 Questions

Look at the execution_table at Step 2. What is the problem with the 'Items' column?

A It contains atomic values

B It has missing values

C It contains multiple values in one field

D It is the primary key

💡 Hint

Check the 'Reason' column in Step 2 of execution_table

At which step does the table first meet First Normal Form (1NF)?

A Step 1

B Step 4

C Step 3

D Step 2

💡 Hint

Look at the 'Reason' column in execution_table for when the table is in 1NF

If we did not split the 'Items' column, what would happen to the number of rows?

A It would stay the same

B It would decrease

C It would increase

D It would become zero

💡 Hint

Check variable_tracker for 'Table Rows' before and after splitting

Concept Snapshot

First Normal Form (1NF):
- Each table column must hold atomic (single) values.
- No repeating groups or arrays in columns.
- Multi-valued fields must be split into separate rows.
- Ensures data is organized for easy querying and updates.

Full Transcript

First Normal Form (1NF) means every column in a database table must have single, atomic values. If a column has multiple values in one field, like a list of items separated by commas, it breaks 1NF. To fix this, we split those multi-valued fields into separate rows so each field holds only one value. This process removes repeating groups and makes the table easier to work with. The example shows a table with an 'Items' column holding multiple items per row. After splitting, each item gets its own row, and the table meets 1NF. This helps keep data clean and consistent.

Practice

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

easy

A. Each table must have a primary key.

B. Tables must have at least two columns.

C. Each column must contain atomic (single) values only.

D. Columns can contain lists or multiple values.

Solution

1. Step 1: Understand 1NF definition

   1NF requires that each column holds only one atomic value per row, no lists or sets.

2. Step 2: Evaluate options

   Each column must contain atomic (single) values only. matches the 1NF rule exactly. Options A, B, and D describe other concepts or violate 1NF.

3. Final Answer:

   Each column must contain atomic (single) values only. -> Option C

4. Quick Check:

   1NF = atomic columns only [OK]

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

Common Mistakes:

• Thinking 1NF requires a primary key
• Allowing lists or sets in columns
• Confusing 1NF with other normal forms

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

easy

A. CREATE TABLE Students (ID INT, Name VARCHAR(50), PhoneNumbers VARCHAR(100));

B. CREATE TABLE Students (ID INT PRIMARY KEY, Name VARCHAR(50), PhoneNumber VARCHAR(15));

C. CREATE TABLE Students (ID INT, Name VARCHAR(50), Email VARCHAR(50));

D. CREATE TABLE Students (ID INT, Name VARCHAR(50), Address VARCHAR(100));

Solution

1. Step 1: Identify 1NF violation in table definitions

   CREATE TABLE Students (ID INT, Name VARCHAR(50), PhoneNumbers VARCHAR(100)); uses PhoneNumbers as VARCHAR(100), likely storing multiple numbers in one field, violating 1NF.

2. Step 2: Check other options

   Options A, B, and C have single atomic values per column, so they follow 1NF.

3. Final Answer:

   CREATE TABLE Students (ID INT, Name VARCHAR(50), PhoneNumbers VARCHAR(100)); -> Option A

4. Quick Check:

   Multiple values in one column break 1NF [OK]

Hint: Multiple values in one column break 1NF [OK]

Common Mistakes:

• Assuming VARCHAR can hold multiple values without issue
• Confusing primary key with 1NF rules
• Ignoring column data types when checking 1NF

3. Given the table below, which row violates First Normal Form (1NF)?

Orders(OrderID, Customer, Items)
Where Items column contains comma-separated product IDs.

Rows:
1. (101, 'Alice', 'P1')
2. (102, 'Bob', 'P2,P3')
3. (103, 'Carol', 'P4')
4. (104, 'Dave', 'P5')

medium

A. Row 1

B. Row 2

C. Row 3

D. Row 4

Solution

1. Step 1: Understand 1NF violation in data rows

   Row 2 has 'P2,P3' in Items, which is multiple values in one cell, violating 1NF.

2. Step 2: Check other rows

   Rows 1, 3, and 4 have single product IDs, so they follow 1NF.

3. Final Answer:

   Row 2 -> Option B

4. Quick Check:

   Multiple values in one cell break 1NF [OK]

Hint: Comma-separated values in one cell break 1NF [OK]

Common Mistakes:

• Ignoring multiple values separated by commas
• Assuming string with commas is atomic
• Not checking all rows carefully

4. You have this table definition violating 1NF:

CREATE TABLE Employees (ID INT, Name VARCHAR(50), Skills VARCHAR(100));

Skills column stores multiple skills separated by commas.
Which SQL change fixes the 1NF violation?

medium

A. Store skills as a single string with semicolons instead of commas.

B. Change Skills to TEXT and store JSON arrays.

C. Keep Skills as VARCHAR but limit length to 50.

D. Create a separate Skills table with EmployeeID and Skill columns.

Solution

1. Step 1: Identify 1NF violation and fix approach

   Storing multiple skills in one column violates 1NF. The fix is to separate repeating data into another table.

2. Step 2: Evaluate options for 1NF compliance

   Create a separate Skills table with EmployeeID and Skill columns. creates a separate Skills table with one skill per row, fixing 1NF. Options B, C, and D still store multiple values in one column.

3. Final Answer:

   Create a separate Skills table with EmployeeID and Skill columns. -> Option D

4. Quick Check:

   Separate repeating data into new table for 1NF [OK]

Hint: Use separate table for repeating groups to fix 1NF [OK]

Common Mistakes:

• Trying to store multiple values in one column anyway
• Using JSON or delimiters inside one column
• Not normalizing repeating data into separate tables

5. You have a table storing orders with multiple products in one column:

Orders(OrderID INT, Customer VARCHAR(50), Products VARCHAR(255))
Products column stores product IDs separated by commas.

How do you redesign the schema to fully comply with First Normal Form (1NF)?

hard

A. Create a new table OrderProducts(OrderID, ProductID) with one product per row.

B. Split Products into multiple columns like Product1, Product2, Product3.

C. Store Products as JSON array in the same column.

D. Keep Products column but restrict to one product ID only.

Solution

1. Step 1: Identify 1NF violation in current design

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

2. Step 2: Choose redesign that enforces atomicity

   Create a new table OrderProducts(OrderID, ProductID) with one product per row. creates a new table with one product per row, fully normalizing the data and satisfying 1NF. Split Products into multiple columns like Product1, Product2, Product3. uses multiple columns but is limited and not scalable. Options C and D still violate 1NF.

3. Final Answer:

   Create a new table OrderProducts(OrderID, ProductID) with one product per row. -> Option A

4. Quick Check:

   Separate repeating data into rows for 1NF compliance [OK]

Hint: Use separate table with one value per row for 1NF [OK]

Common Mistakes:

• Adding multiple columns instead of rows
• Using JSON or arrays inside one column
• Restricting to one product but losing data