mysql - InnoDB，如何检测索引类型？

Question

我有一张 table :

CREATE TABLE  `posts` (
  `post_id` mediumint(8) unsigned NOT NULL AUTO_INCREMENT,
  `topic_id` mediumint(8) unsigned NOT NULL DEFAULT '0',
  `forum_id` mediumint(8) unsigned NOT NULL DEFAULT '0',
  `poster_id` mediumint(8) unsigned NOT NULL DEFAULT '0',
  `icon_id` mediumint(8) unsigned NOT NULL DEFAULT '0',
  `poster_ip` varchar(40) COLLATE utf8_bin NOT NULL DEFAULT '',
  `post_time` int(11) unsigned NOT NULL DEFAULT '0',
  `post_approved` tinyint(1) unsigned NOT NULL DEFAULT '1',
  `post_reported` tinyint(1) unsigned NOT NULL DEFAULT '0',
  `enable_bbcode` tinyint(1) unsigned NOT NULL DEFAULT '1',
  `enable_smilies` tinyint(1) unsigned NOT NULL DEFAULT '1',
  `enable_magic_url` tinyint(1) unsigned NOT NULL DEFAULT '1',
  `enable_sig` tinyint(1) unsigned NOT NULL DEFAULT '1',
  `post_username` varchar(255) COLLATE utf8_bin NOT NULL DEFAULT '',
  `post_subject` blob,
  `post_text` mediumtext COLLATE utf8_bin NOT NULL,
  `post_checksum` varchar(32) COLLATE utf8_bin NOT NULL DEFAULT '',
  `post_attachment` tinyint(1) unsigned NOT NULL DEFAULT '0',
  `bbcode_bitfield` varchar(255) COLLATE utf8_bin NOT NULL DEFAULT '',
  `bbcode_uid` varchar(8) COLLATE utf8_bin NOT NULL DEFAULT '',
  `post_postcount` tinyint(1) unsigned NOT NULL DEFAULT '1',
  `post_edit_time` int(11) unsigned NOT NULL DEFAULT '0',
  `post_edit_reason` varchar(255) COLLATE utf8_bin NOT NULL DEFAULT '',
  `post_edit_user` mediumint(8) unsigned NOT NULL DEFAULT '0',
  `post_edit_count` smallint(4) unsigned NOT NULL DEFAULT '0',
  `post_edit_locked` tinyint(1) unsigned NOT NULL DEFAULT '0',
  PRIMARY KEY (`post_id`),
  KEY `forum_id` (`forum_id`),
  KEY `topic_id` (`topic_id`),
  KEY `poster_ip` (`poster_ip`),
  KEY `poster_id` (`poster_id`),
  KEY `post_approved` (`post_approved`),
  KEY `post_username` (`post_username`),
  KEY `tid_post_time` (`topic_id`,`post_time`) USING HASH
) ENGINE=InnoDB AUTO_INCREMENT=22381 DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

如您所见，最后一个索引是“USING HASH”——但是当我使用show indexes from posts; 时，并没有显示它

Answer 1

经过快速Google search , 我很快发现 InnoDB doesn't support HASH indexes , 但仍然接受表定义中的修饰符。

SHOW CREATE TABLE 可能会显示 USING HASH，但是 SHOW INDEXES实际上会告诉你正在使用什么索引类型:

Index_type

The index method used (BTREE, FULLTEXT, HASH, RTREE).