$conn->query("CREATE TRIGGER `before_delete_conversation` BEFORE DELETE ON `T_H_CONVERSATION_COV` FOR EACH ROW DELETE FROM T_H_MESSAGE_MSG WHERE PK_ID = (SELECT FK_MESSAGE
$conn->query("CREATE TRIGGER `before_delete_conversation` BEFORE DELETE ON `T_H_CONVERSATION_COV` FOR EACH ROW DELETE FROM T_H_MESSAGE_MSG WHERE PK_ID = (SELECT FK_MESSAGE