有表结构如下:
CREATE TABLE `member` ( …… userid char(11) NOT NULL DEFAULT '' , KEY ind_ userid (userid)…… ) ENGINE=InnoDB;
执行计划如下:
mysql> explain extended select username from`member` where userid =13772556391 limit 0,1;
mysql> show warnings;
Warning1:Cannot use index 'ind_userid' due to type or collation conversion on field ' userid' Note:select `member`.`username` from `member` where (`member`.`userid` = 13772556391) limit 0,1
请给出原因及优化方案