mysql插入数据时检查是否某字段已存在

SELECT\n" +
                                                                    "	'',\n" +
                                                                    "	'{0}',\n" +
                                                                    "	'{1}',\n" +
                                                                    "	'{2}'\n" +
                                                                    "FROM\n" +
                                                                    "	DUAL\n" +
                                                                    "WHERE\n" +
                                                                    "	NOT EXISTS (\n" +
                                                                    "		SELECT\n" +
                                                                    "			字段0\n" +
                                                                    "		FROM\n" +
                                                                    "			表\n" +
                                                                    "		WHERE\n" +
                                                                    "			字段0= '{0}'\n" +
                                                                    "	)";