Both Mandatory
The One to One (1:1) relationship is used when there is a maximum participation of one on either side of the relationship. If possible, the application will combine the entities related by a 1:1 relationship. In situations where the tables cannot be combined, the application will apply the Foreign Key Rules. Unlike the One to Many, the placement of the foreign key depends on several factors (see Foreign Key Rules). Consider the constraints that are applied to the foreign key of the entity that receives the foreign key under the following scenarios:
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Both Mandatory |
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Both Optional |
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Optional and Mandatory |
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Mandatory and Optional |
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See also: Many to Many, One to Many, Weak, Specialization and Foreign Key Rules
