III.1.2. First Normal Form: No Repeating Groups
The first normal form states that no repeating elements or groups of elements can exist within the tables. Additionally, it states that each column is atomic. These rules can be summarized as:
More than one value is not allowed in any cell (a repeating group within a column). A column for the product purchased, can include only one product purchased. Two products can't be in the same column.
More than one column is not used to define the same piece of data (a repeating group across columns). If more than one product is purchased, it's not in the same table as Product1, Product2, and so on.
Columns must be atomic. Data within a column is broken down into the smallest meaningful element. A Name column would be divided into three columns as First Name, Middle Name, and Last Name.
III.1.2.1. No repeating groups within a column
A repeating group within a column is a group where more than one value is included in a single column.
For example, consider a table used to record sales information. For every sale, the table owner desires to record the customer's name, the date, and the item purchased.
Violating the first normal form, a table similar to Figure 1-1 could be created. Three columns (ItemDescription, ItemQty, and ItemPrice) have repeating groups. The customer purchased two books, and both book descriptions are in the ItemDescription column. Additionally, both quantities are in the ItemQty column, and both prices are in the ItemPrice ...