# Because of its unique role, the primary column is limited to data types and formula outputs that result in alphanumeric characters.

In Spreadsheet.com, the Primary column of a worksheet plays a special role. Entries in the primary column act as identifiers for each row, with this unique identifier appearing when rows are expanded, when rows are Related between worksheets, or as the display name on Kanban cards.

Because of its unique role, the primary column is limited to data types and formula outputs that result in alphanumeric characters. For instance, primary columns cannot contain Attachment files or Users (either directly or as the output of formulas).

## Formulas in the Primary Column

Like with other columns, you can create or edit a formula for the primary column. However, the output of the formula must be alphanumeric and you may wish to pick formulas that can result in a unique identifier.

Although the primary column's data types are limited, you can use any function you'd like in the primary column.

## The Column formula Data Type in the Primary Column

If you want every value in the primary column to be determined by the same formula, a Column formula data type might be your best option. The column formula data type applies a formula for every table cell in your column and can reference other cells in each row. Like other formulas and data types, it can be used in the primary column as long as its output is an alphanumeric value. Learn more in our article on the Column formula data type.

Check out our article on The Primary Column for more information about what the primary column can do. Or, take a look at our articles on formulas for more about creating and applying formulas.