A referential integrity constraint violation occurs if an R-tuple refers to an undefined identifier (i.e. there is no E-tuple identified by this foreing key). Violations can be repaired or ignored.
referential_integrity_repair. If the value is
add, then the defective E-tuple is added. If the value is
deletethen the offending R-tuple is deleted. If the value is
ignorean exception is raised: simply don't call this predicate if no check should be performed.