In a related case, the foreign key of one table may reference the primary key of a second table. The second table also has a foreign key, and it references the primary key of the first table. This is known as cross-referencing foreign keys.
Cross-referencing and self-referencing foreign keys are a special case of Referential Integrity. While not well known, they have many real world uses.
FirstSQL fully supports both types and provides additional facilities and syntax to ease use of self-referencing and cross-referencing foreign keys. FirstSQL also supports more extended cross-referencing situations where more than 2 tables are chained together.
For a general discussion of self-referencing and cross-referencing referential integrity, see the Technical Article: Extended Referential Integrity.
Next section Conclusion: Can Your Database Protect Your Data with Complete Referential Integrity?.
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