This is where you have two tables and each record on one table has one and only one corresponding record on the other. To connect them, they both have a corresponding code, that is unique in each...
Here is Example!!
Entity: PERSON
Att:Baby_Name, Father_Name
Entity: CITY
Att: Country_Name, City_Name, Hospital_Name
1 To 1 Relation:
One Baby born at one place(Hospital).
A one-to-one relationship in a database implies that for one occurrence of a parent entity, there is one and only one child table entry. Note that the one-to-one relationship may be tagged as 0 or 1...