MySQL-解释一条sql语句的执行

Question

建news表, id为主键, created上建索引.当使用InnoDB引擎时:

mysql> explain SELECT id, title, summary, created FROM news ORDER BY created DESC LIMIT 10000, 10;
    +----+-------------+-------+------+---------------+------+---------+------+--------+----------------+
    | id | select_type | table | type | possible_keys | key  | key_len | ref  | rows   | Extra          |
    +----+-------------+-------+------+---------------+------+---------+------+--------+----------------+
    |  1 | SIMPLE      | news  | ALL  | NULL          | NULL | NULL    | NULL | 100447 | Using filesort |
    +----+-------------+-------+------+---------------+------+---------+------+--------+----------------+
    1 row in set (0.01 sec)

Answer 1

我记得 InnoDB 只能给MySql 查询优化器 返回 一个估计的结果, 所以会有一些偏差. 而MyISAM给的结果是准确的.