我的查询很简单：EXPLAIN SELECT * FROM de_company WHERE username='hzsanli';(username='hzsanli'这条记录在数据表里是存在的;)
显示如下：
id select_type TABLE TYPE possible_keys key_len ref ROWS extra
1 SIMPLE de_company const username 62 const
SELECT LENGTH(`username`),`username` FROM de_company ORDER BY LENGTH(`username`) ASC LIMIT 200;显示有username为空的记录；
数据结构如下：
create table
CREATE TABLE `de_company` (
`company_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`userid` bigint(20) unsigned NOT NULL DEFAULT '0',
`username` varchar(30) NOT NULL DEFAULT '',
`groupid` smallint(4) unsigned NOT NULL DEFAULT '0',
`company` varchar(100) NOT NULL DEFAULT '',
`level` tinyint(1) unsigned NOT NULL DEFAULT '0',
`validated` tinyint(1) unsigned NOT NULL DEFAULT '0',
`validator` varchar(100) NOT NULL DEFAULT '',
`validtime` int(10) unsigned NOT NULL DEFAULT '0',