ORDER BY _column1, _column2; /* _column1升序，_column2升序 */
ORDER BY _column1, _column2 DESC; /* _column1升序，_column2降序 */
ORDER BY _column1 DESC, _column2 ; /* _column1降序，_column2升序 */
ORDER BY _column1 DESC, _column2 DESC; /* _column1降序，_column2降序 */