Database 1NF First Normal Form

1nf.md

First Normal Form or 1NF

• Database table values must be atomic. That is, the value represented can not be decomposed any further. eg two diferent phone numbers is the telephone field.
• Database table must be isomorphic. A table is isomorphic to some relation if the following are met:

1. order of rows has no meaning
2. column order has no meaning
3. there are no duplicate rows
4. Every row and column intersection has a value (null is considered a value)
5. All columns are regular (no hidden components)

https://en.wikipedia.org/wiki/First_normal_form

2nf.md

Second Normal Form or 2NF

A database is said to be in Second Normal Form if:

1. The database meets 1NF requirements
2. Each column in a table represents what the primary key is describing.

"... when a table is in second normal form, it has a single purpose ..."

https://www.essentialsql.com/get-ready-to-learn-sql-10-database-second-normal-form-explained-in-simple-english/

3nf.md

Third Norml Form or 3NF

A database is said to be in Third Normal Form if:

1. The databse meets 2NF requirements
2. Any column, that is not the primary key, is not dependent on any other column.

For example, a table with a date of birth column and an age column. The age column breaks this rule as its value depends on the date of birth column.

https://www.essentialsql.com/get-ready-to-learn-sql-11-database-third-normal-form-explained-in-simple-english/ https://en.wikipedia.org/wiki/Third_normal_form