Use the Field Flags to set the field properties, described below.
Allow Null
Allow the NULL values for the field.
Note: To set NULL and Empty String as default value, see Setting Other Field Properties.
Primary Key
A Primary Key is a single field or combination of fields that uniquely defines a record. None of the fields that are part of the primary key can contain a null value.
Primary Key Name
Right-click and select Primary Key Name from the popup menu to enter the primary key constraint name.