First Normal Form (1NF)

First Normal Form (1NF)

A table is in 1NF if every column contains only atomic (indivisible) values and there are no repeating groups. Each cell must hold a single value, not a list or set.

Violation of 1NF

  NOT in 1NF: Repeating groups
  ┌────┬─────────┬──────────────────────────┐
  │ ID │ Name    │ Courses                  │
  ├────┼─────────┼──────────────────────────┤
  │ 1  │ Alice   │ Databases, Networking    │
  │ 2  │ Bob     │ Databases, OS            │
  └────┴─────────┴──────────────────────────┘

  Problems:
  • "Databases, Networking" is NOT atomic — it's two values in one cell
  • Can't query efficiently: WHERE Courses = 'Databases'
  • Can't index individual courses

Converting to 1NF

  IN 1NF: One value per cell

  Option 1: Separate rows
  ┌────┬─────────┬────────────┐
  │ ID │ Name    │ Course     │
  ├────┼─────────┼────────────┤
  │ 1  │ Alice   │ Databases  │
  │ 1  │ Alice   │ Networking │
  │ 2  │ Bob     │ Databases  │
  │ 2  │ Bob     │ OS         │
  └────┴─────────┴────────────┘

  Option 2: Separate tables (better — fully normalized)
  Students              Enrollments           Courses
  ┌────┬─────────┐     ┌────┬─────────┐     ┌────┬────────┐
  │ ID │ Name    │     │SID │CrsID    │     │ ID │ Title  │
  ├────┼─────────┤     ├────┼─────────┤     ├────┼────────┤
  │ 1  │ Alice   │     │ 1  │ 101     │     │101 │ DB     │
  │ 2  │ Bob     │     │ 1  │ 102     │     │102 │ Net    │
  └────┴─────────┘     │ 2  │ 101     │     │103 │ OS     │
                       │ 2  │ 103     │     └────┴────────┘
                       └────┴─────────┘

Rules for 1NF

• Each column must contain atomic values (no lists, no sets).
• Each row must be unique (have a primary key).
• Each column must contain values of a single type.
• Column names must be unique within the table.