First Normal Form (1NF)

A table is considered to be in 1NF if:

1. There is no top-to-bottom ordering to the rows
2. There is no left-to-right ordering to the columns
3. There are no duplicate rows
4. Every row-and-column intersection contains exactly one value^*
5. All columns are regular (no hidden components)

A table without a unique key (meaning that duplicate rows could exist) or a table with a nullable column (a violation of condition 4) would not be in 1NF.


^*Condition 4, which does not allow repeating groups, is thought by many to be the defining feature of 1NF.