rental表的存儲引擎是innodb， rental_myisam表的存儲引擎是myisam。兩張表除存儲引擎不同外，表結構都一樣。CREATE?TABLE?`rental`?( ??`rental_id`?int(11)?NOT?NULL?AUTO_INCREMENT, ??`rental_date`?datetime?NOT?NULL, ??`inventory_id`?mediumint(8)?unsigned?NOT?NULL, ??`customer_id`?smallint(5)?unsigned?NOT?NULL, ??`return_date`?datetime?DEFAULT?NULL, ??`staff_id`?tinyint(3)?unsigned?NOT?NULL, ??`last_update`?timestamp?NOT?NULL?DEFAULT?CURRENT_TIMESTAMP?ON?UPDATE?CURRENT_TIMESTAMP, ??PRIMARY?KEY?(`rental_id`), ??KEY?`rental_date`?(`rental_date`,`inventory_id`,`customer_id`) )?ENGINE=innodb?DEFAULT?CHARSET=utf8; CREATE?TABLE?`rental_myisam`?( ??`rental_id`?int(11)?NOT?NULL?AUTO_INCREMENT, ??`rental_date`?datetime?NOT?NULL, ??`inventory_id`?mediumint(8)?unsigned?NOT?NULL, ??`customer_id`?smallint(5)?unsigned?NOT?NULL, ??`return_date`?datetime?DEFAULT?NULL, ??`staff_id`?tinyint(3)?unsigned?NOT?NULL, ??`last_update`?timestamp?NOT?NULL?DEFAULT?CURRENT_TIMESTAMP?ON?UPDATE?CURRENT_TIMESTAMP, ??PRIMARY?KEY?(`rental_id`), ??KEY?`rental_date`?(`rental_date`,`inventory_id`,`customer_id`) )?ENGINE=MyISAM?DEFAULT?CHARSET=utf8;使用explain分析，發現?rental表?使用了主鍵索引排序，而?rental_myisam表?卻并沒有用到主鍵索引排序，反而extra里用到"文件排序"，不太懂為啥會是這樣的區別？explain select * from rental where return_date > '2005-08-30' order by rental_idGexplain select * from rental_myisam where rental_date > '2005-01-01' order by rental_id\G