bitscn.com
如表： user字段： userid name pw本来user表的useid不是自增的。 我们把userid改为自增。执行以下语句就可以把userid自增， 每次加1。语句：alter table `user` change userid userid int not null auto_increment primary key; 表的sql：
create table `user` (
`username` varchar(20) not null,
`pw` varchar(20) not null,
`userid` int(11) not null auto_increment,
primary key (`userid`)
) engine=innodb default charset=utf8;
扩展知识：//添加字段并设置主键alter table tabelname add new_field_id int(5) unsigned default 0 not null auto_increment ,add primary key (new_field_id);//加主关键字的索引alter table tablename add primary key(id);//加索引 www.bitscn.com alter table tablename change depno depno int(5) not null;alter table tablename add index 索引名 (字段名1[，字段名2 …]);alter table tablename add index emp_name (name);//加唯一限制条件的索引alter table tablename add unique emp_name2(cardnumber);//删除某个索引alter table tablename drop index emp_name; //增加字段：alter table table_name add field_name field_type;//删除字段alter table table_name drop field_name;//重命名列alter table table_name change field_name1 field_name2 integer;//调整字段顺序 alter table `users` change `user_password` `user_password` varchar( 20 ) not null after user_name;//改变列的类型alter table table_name change field_name field_name bigint not null;alter table infos change list list tinyint not null default '0';//修改原字段名称及类型： www.bitscn.com alter table table_name change old_field_name new_field_name field_type;//重命名表alter table table_name rename new_table_name;//级联更新 和 删除(红色部分,不区分大小写 )drop table if exists `mail_model`;create table mail_model(id varchar(50) primary key not null ,mail_filename varchar(200),content varchar(2000))engine=innodb default charset=gbk;drop table if exists `mail_model_extend`;create table mail_model_extend(id int(6) auto_increment not null primary key,rid varchar(50) not null,content varchar(2000),index (rid),foreign key (rid) references mail_model(id) on delete cascade on update cascade)engine=innodb default charset=gbk;
bitscn.com