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What is referential integrity in a relational database?
A rule that requires foreign key values to either fully match or match some primary key value.
What happens if a primary key is updated in a relational database?
It may violate referential integrity unless actions like RESTRICT, SET NULL, SET DEFAULT, or CASCADE are applied.
How is a composite key defined in terms of null values?
A composite key value is partially null if some but not all columns are null.
What is the effect of deleting a foreign key on its corresponding primary key?
Deleting a foreign key has no effect on the primary key.
What does the RESTRICT action do in referential integrity?
It rejects an insert, update, or delete that violates referential integrity.
What is the CASCADE action in referential integrity?
It propagates primary key changes to foreign keys; if a primary key is deleted, matching foreign keys are also deleted.
What does SET DEFAULT do in referential integrity actions?
It sets invalid foreign keys to the foreign key default value.
Can a null in a simple foreign key violate referential integrity?
No, a null in a simple foreign key does not violate referential integrity.
What happens if a primary key is deleted in relation to foreign keys?
If the primary key is deleted, rows containing matching foreign keys are deleted.
