= Additional Integrity Constraints =

== Description ==

This section documents additional CHECK and UNIQUE constraints implemented during the advanced database development phase.

The constraints improve data integrity by restricting invalid values and preventing duplicate RSVP and attendance records.

=== SQL Code ===

{{{
#!sql
ALTER TABLE event_rsvp
ADD CONSTRAINT chk_rsvp_status
CHECK (status IN ('accepted', 'declined', 'pending'));

ALTER TABLE attendance
ADD CONSTRAINT chk_attendance_status
CHECK (status IN ('attending', 'absent'));

ALTER TABLE event_rsvp
ADD CONSTRAINT uq_guest_event_rsvp
UNIQUE (guest_id, event_id);

ALTER TABLE attendance
ADD CONSTRAINT uq_guest_event_attendance
UNIQUE (guest_id, event_id);
}}}

== Constraint Overview ==

* CHECK constraints restrict invalid RSVP and attendance status values.
* UNIQUE constraints prevent duplicate RSVP submissions for the same guest and event.
* UNIQUE constraints also prevent duplicate attendance records for the same guest and event.
* Integrity rules are enforced directly at database level independently from the application layer.

== Summary ==

The additional integrity constraints improve consistency, reliability, and validation safety inside the Wedding Planner Management System database schema.