ALTER TABLE wcf1_conversation ADD FOREIGN KEY (userID) REFERENCES wcf1_user (userID) ON DELETE SET NULL;
ALTER TABLE wcf1_conversation ADD FOREIGN KEY (lastPosterID) REFERENCES wcf1_user (userID) ON DELETE SET NULL;
ALTER TABLE wcf1_conversation ADD FOREIGN KEY (firstMessageID) REFERENCES wcf1_conversation_message (messageID) ON DELETE SET NULL;
ALTER TABLE wcf1_conversation_to_user ADD FOREIGN KEY (conversationID) REFERENCES wcf1_conversation (conversationID) ON DELETE CASCADE;
ALTER TABLE wcf1_conversation_to_user ADD FOREIGN KEY (participantID) REFERENCES wcf1_user (userID) ON DELETE SET NULL;
ALTER TABLE wcf1_conversation ADD FOREIGN KEY (userID) REFERENCES wcf1_user (userID) ON DELETE SET NULL;
ALTER TABLE wcf1_conversation ADD FOREIGN KEY (lastPosterID) REFERENCES wcf1_user (userID) ON DELETE SET NULL;
ALTER TABLE wcf1_conversation ADD FOREIGN KEY (firstMessageID) REFERENCES wcf1_conversation_message (messageID) ON DELETE SET NULL;
ALTER TABLE wcf1_conversation_to_user ADD FOREIGN KEY (conversationID) REFERENCES wcf1_conversation (conversationID) ON DELETE CASCADE;
ALTER TABLE wcf1_conversation_to_user ADD FOREIGN KEY (participantID) REFERENCES wcf1_user (userID) ON DELETE SET NULL;