Primary column
By default, every table contains a Primary column used to reference the table row within the user interface. Typically, the Primary column stores the name description of the data that is stored in a table's row and is a single line of text column. The Primary column is the first column that is listed and available so you have a way to identify a record in a table.
You can see the Primary column in various places in a model-driven app such within lookup columns, the header of a row form, and in the window title of the browser.
The Primary column isn't the same as the unique identifier key column that is also autogenerated when you create a new custom table. The Unique identifier column is a GUID.
Note
The Unique identifier column isn't called "Unique identifier" by name. It bears the same name as the table. For example if you table name is "Pet", your primary key column will have the name "Pet" and will be displayed as a GUID.
You can only update the schema name and display name of the Primary column until you create the table. After the table is created, you can't update the schema name. You can change the display name of the Primary column to make it friendlier for business users.
After creating a table, you can do some editing of the Primary column, such as to change its data type, choosing between a plain text column or an autogenerated string.
Tip
If you want to make the primary column unique, then create an alternate key and assign the Primary Name column to the new key.