CREATE TABLE invitations (
    id VARCHAR(64) PRIMARY KEY DEFAULT uuid_generate_v4(),
    sender_id VARCHAR(64) REFERENCES users(id) ON DELETE CASCADE,
    receiver_id VARCHAR(64) REFERENCES users(id) ON DELETE CASCADE,
    music_session_id VARCHAR(64) REFERENCES music_sessions(id) ON DELETE CASCADE,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
);

ALTER TABLE invitations ADD CONSTRAINT invitations_uniqkey UNIQUE (sender_id, receiver_id, music_session_id);