Index: advanced_constraints.sql
===================================================================
--- advanced_constraints.sql	(revision 3679996aa9694cc6afa7598db54bdc53f0f651fb)
+++ advanced_constraints.sql	(revision 3679996aa9694cc6afa7598db54bdc53f0f651fb)
@@ -0,0 +1,15 @@
+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);