One - to - one ( data model ) - Wikipedia One - to - one ( data model ) A country has only one capital city, and a capital city is the capital of only one country In systems analysis, a one - to - one relationship is a type of cardinality that refers to the relationship between two entities ( see also entity -- relationship model ) A and B in which one element of A may only be linked to one element of B, and vice versa. For instance, think of A as countries, and B as capital cities. A country has only one capital city, and a capital city is the capital of only one country. In a relational database, a one - to - one relationship exists when one row in a table may be linked with only one row in another table and vice versa. It is important to note that a one - to - one relationship is not a property of the data, but rather of the relationship itself. A list of mothers and their children may happen to describe mothers with only one child, in which case one row of the mothers table will refer to only one row of the children table and vice versa, but the relationship itself is not one - to - one, because mothers may have more than one child, thus forming a one - to - many relationship. See also One - to - many ( data model ) Many - to - many ( data model ) References External links Design pattern : many - to - many ( order entry ), Tomjewett.com This systems - related article is a stub. You can help Wikipedia by expanding it. Retrieved from `` https://en.wikipedia.org/w/index.php?title=One-to-one_(data_model)&oldid=837074718 '' Categories : Data modeling Systems theory stubs Talk About Wikipedia Add links This page was last edited on 18 April 2018, at 15 : 25. About Wikipedia

Question: what is a one to one relationship in a database
Answer: when one row in a table may be linked with only one row in another table and vice versa