Interaction of Constraints - Firebird

By combining the formal referential constraint with other integrity constraints it is possible to implement most, if not all, of your business rules with a high degree of precision. For example, a NOT NULL column constraint will restrict the action options and prevent orphan rows, if required, whereas a foreign key column that is nullable can be used to implement special data structures such as trees (see the section “Self-Referencing Relationships”).

Referential constraints can be assisted by CHECK constraints. In some cases, a CHECK constraint inherited from a domain could interfere or conflict with a referential constraint, too. It is worth spending a few minutes sketching out the effects of each con- straint on paper or a whiteboard, to identify and eliminate any potential problems.

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