Database Reference
In-Depth Information
One-to-One Relationships
A pair of tables bears a
one-to-one
relationship when a single record in the first table is re-
latedto
only one
recordinthesecondtable,andasinglerecordinthesecondtableisrelated
to
only one
record in the first table.
Figure 10.3
shows a generic example of a one-to-one
relationship.
Figure 10.3. A generic example of a one-to-one relationship
As you can see, a single record in TABLE A is related to only one record in TABLE B,
and a single record in TABLE B is related to only one record in TABLE A. A one-to-one
relationshipusually(butnotalways)involvesa
subset
table.
Figure10.4
showsanexample
of a typical one-to-one relationship that you might find in a database for an organization's
human resources department. This example also illustrates a situation where neither of the
tables is a subset table.
