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"rpond" <novahokie_at_gmail.com> wrote in message
news:1109114043.273191.51590_at_f14g2000cwb.googlegroups.com...
> 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. Received on Tue Feb 22 2005 - 17:23:30 CST