How to understand the mySQL syntax "KEY `node_type` (`type`(4))"?

Question

MySQL

I dumped a Drupal node table, I want to use it in my Yii project,

CREATE TABLE IF NOT EXISTS `node` (
  `nid` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT 'The primary identifier for a node.',
  `vid` int(10) unsigned DEFAULT NULL COMMENT 'The current node_revision.vid version identifier.',
  `type` varchar(32) NOT NULL DEFAULT '' COMMENT 'The node_type.type of this node.',
  `language` varchar(12) NOT NULL DEFAULT '' COMMENT 'The languages.language of this node.',
  `title` varchar(255) NOT NULL DEFAULT '' COMMENT 'The title of this node, always treated as non-markup plain text.',
  `uid` int(11) NOT NULL DEFAULT '0' COMMENT 'The users.uid that owns this node; initially, this is the user that created it.',
  `status` int(11) NOT NULL DEFAULT '1' COMMENT 'Boolean indicating whether the node is published (visible to non-administrators).',
  `created` int(11) NOT NULL DEFAULT '0' COMMENT 'The Unix timestamp when the node was created.',
  `changed` int(11) NOT NULL DEFAULT '0' COMMENT 'The Unix timestamp when the node was most recently saved.',
  `comment` int(11) NOT NULL DEFAULT '0' COMMENT 'Whether comments are allowed on this node: 0 = no, 1 = closed (read only), 2 = open (read/write).',
  `promote` int(11) NOT NULL DEFAULT '0' COMMENT 'Boolean indicating whether the node should be displayed on the front page.',
  `sticky` int(11) NOT NULL DEFAULT '0' COMMENT 'Boolean indicating whether the node should be displayed at the top of lists in which it appears.',
  `tnid` int(10) unsigned NOT NULL DEFAULT '0' COMMENT 'The translation set id for this node, which equals the node id of the source post in each set.',
  `translate` int(11) NOT NULL DEFAULT '0' COMMENT 'A boolean indicating whether this translation page needs to be updated.',
  PRIMARY KEY (`nid`),
  UNIQUE KEY `vid` (`vid`),
  KEY `node_changed` (`changed`),
  KEY `node_created` (`created`),
  KEY `node_frontpage` (`promote`,`status`,`sticky`,`created`),
  KEY `node_status_type` (`status`,`type`,`nid`),
  KEY `node_title_type` (`title`,`type`(4)),
  KEY `node_type` (`type`(4)),
  KEY `uid` (`uid`),
  KEY `tnid` (`tnid`),
  KEY `translate` (`translate`),
  KEY `language` (`language`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COMMENT='The base table for nodes.' AUTO_INCREMENT=195 ;

I'm scratching my head what do the fours in key mean?

KEY `node_title_type` (`title`,`type`(4)),
  KEY `node_type` (`type`(4)),

Answer 1

well, it is obvious that the first 4 characters of the value of the type field are used