A worksheet's primary column provides a unique identifier to identify rows when they are expanded, related, or included in a Kanban view.
A worksheet's primary column is the column used to uniquely identify rows and is demarcated with a key icon: 
. This unique identifier or display name appears when rows are expanded, when rows are related between worksheets, or as the display name on Kanban cards. The primary column is also where row hierarchies are established.
Only columns of certain data types can serve as the primary column.
Rows have a unique row – the table header row – too, which is used to delineate between header information and table data.
Setting or Changing the Primary Column
By default, the first column of a worksheet is the primary column. You can designate a different column as the primary one by right clicking on the column header or clicking the downward arrow to the right of the column name and selecting "Set as primary column" from the dropdown.
Only users with Owner or Manager access in a workbook can change that workbook's primary column.
The "Set as primary column" option will be greyed out when the desired column is currently set to a restricted data type, detailed below. To make the "Set as primary column" option available, you must change the column's data type to a compatible option, or pick a different column to use as your primary column.
Primary Column Data Type Restrictions
The primary column only supports alphanumeric data types. The data types that can be used in the primary column are:
- Automatic
- Text
- Number
- Currency
- Percent
- Date
- Date & time
- Duration
- URL
- Phone
- Autonumber
- Column formula
While editing the data type of the primary column, you can change its data type to other alphanumeric data types only. Conversely, a column with any of the following data types cannot be designated as a primary column: Attachment, Related row, User, Checkbox, Select, Multiselect, Rating, Icon set, Related row lookup, and System columns (like Updated by and Created at).
While the primary column can have empty or duplicate values, it is best practice to ensure that the cell values in the primary column are filled to help in uniquely identifying rows. You can use the Autonumber data type to avoid duplicate values in the primary column.
Expanded Rows and the Primary Column
When you expand a row, the primary column value will be used as the identifier at the top of the expanded row dialog.
Similarly, the primary column also provides the display name for the row's card in a Kanban view.
Row Hierarchies and the Primary Column
The primary column is also used to define row hierarchies. Row hierarchies allow you to define and organize tasks and sub-tasks by creating "parent" and "child" rows. Row hierarchies are useful when you have rows of data that are related to each other, like denoting subtasks in a project plan or budget line items that roll-up to subtotals.
For more insight into row hierarchies, see our article on creating row hierarchies.
Related Rows and the Primary Column
One unique feature of Spreadsheet.com is that you can relate data between worksheets. This allows you to store all of your data in one source, but reference it in others. In cases where this related row relationship is defined, the cell values in primary columns serve as labels for the entire row. Any changes made to cell values in the primary column are automatically synced to all related sheet cells.
For more information about working with Related Rows, see our suite of articles about establishing relationships between worksheets.
Continue reading to learn more about managing columns, including inserting and moving them, copying them, and freezing them.