小编aho*_*hoo的帖子

我在Mysql中运行了一个查询,如下所示:

EXPLAIN
SELECT *
FROM(
        SELECT *  # Select Number 2
        FROM post
        WHERE   parentid = 13
        ORDER BY time, id
        LIMIT 1, 10
    ) post13_childs
JOIN post post13_childs_childs
ON post13_childs_childs.parentid = post13_childs.id

结果是:

id |select_type  |table               |type |possible_keys  |key      |key_len  |ref              |rows    |Extra
1  |PRIMARY      |<derived2>          |ALL  | NULL          | NULL    |NULL     |NULL             |10      |
1  |PRIMARY      |post13_childs_childs|ref  |parentid       |parentid |9        |post13_childs.id |10      |Using where
2  |DERIVED      |post                |ALL  |parentid       |parentid |9        |                 |153153  |Using where; Using filesort

这意味着它使用了索引, …

假设我有两个下表:

CREATE TABLE post (
  id bigint(20)     NOT NULL    AUTO_INCREMENT,
  text text ,

  PRIMARY KEY (id)
) ENGINE=InnoDB AUTO_INCREMENT=1;

CREATE TABLE post_path (
  ancestorid bigint(20)     NOT NULL    DEFAULT '0',
  descendantid bigint(20)   NOT NULL    DEFAULT '0',
  length int(11)            NOT NULL    DEFAULT '0',

  PRIMARY KEY (ancestorid,descendantid),
  KEY descendantid (descendantid),

  CONSTRAINT f_post_path_ibfk_1 
    FOREIGN KEY (ancestorid) REFERENCES post (id) 
    ON DELETE CASCADE 
    ON UPDATE CASCADE,
  CONSTRAINT f_post_path_ibfk_2 
    FOREIGN KEY (descendantid) REFERENCES post (id) 
    ON DELETE CASCADE 
    ON UPDATE CASCADE
) ENGINE=InnoDB;

并插入这些行:

INSERT INTO …

我在这里找到了sql server中的答案,但我的问题是在mysql中.请帮我