FK versus PK

"rpond" wrote in message

 > Database beginner here,
 >
 > What does it mean when a column is both a primary key and a foreign key?
 >
The column uniquely identifies the row on the table where it is the primary
key. If the column is also a foreign key, then that value must exist as the
primary key on another table. So in effect, both tables have the same
primary key, but one of the tables is the parent of the other table (parent
row must exist for each child in the other table).

This may not be proper 3rd normal form, but there are sometimes reasons for
having two tables with the same primary key.
 >> Stay informed about: FK versus PK 

"David Aldridge" wrote in message

 > It could also be the case that the column is only part of the primary
 > key and is also a foreign key ... that would probably be a more common
 > case.
 >

..... such as ORDER_ID and ITEM_NO as a 2-column PK in a dependent table
(ORDER_ITEMS dependent on ORDERS) with ORDER_ID being the FK to ORDERS

++ mcs
 >> Stay informed about: FK versus PK