The rules for First Normal Form are:
Every column must be atomic. It cannot be decomposed into two or more subcolumns.
You cannot have multivalued columns or repeating groups.
Each row and column position can have only one value.
The table in Figure 6-1 violates First Normal Form, since the dept_no column contains a repeating group:
Figure 6-1: A table that violates first Normal Form
Normalization creates two tables and moves dept_no to the second table:
Figure 6-2: Correcting First Normal Form violations by creating two tables