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 */