For example, the "Doctor Last Name" field might be assigned as a primary key of the Doctor table with all people having same last name organized alphabetically according to the first three letters of their first name. A table can also have a foreign key which indicates that  field is linked to the primary key of another table.
For instance, the "Doctor Last Name" field can be used as the primary key for the Doctor table, organizing people with the same last name alphabetically based on their first three letters. Similarly, a table may contain a foreign key that references the primary key of another table.