mysql----id主键列乱了之后,重新排序

https://blog.csdn.net/weixin_42321963/article/details/82751622

实例如下:

第一步:

创建表如下:

create table category(
cid int(3)unsigned auto_increment primary key,
cname varchar(20) unique
);
第二步:

插入数据,并查询:

insert into category values(null,'衣服');
insert into category values(null,'皮包');
insert into category values(null,'手表');
insert into category values(null,'lala');
 
select * from category  order by cid  ;



第三步:重复插入:

insert into category values(null,'衣服');
insert into category values(null,'皮包');
insert into category values(null,'手表');
insert into category values(null,'lala');


第四步:

插入并查询结果:

insert into category values(null,'nba');


产生变化了,中间断层了,

第五步:

重新排序:并查询:

alter table category drop cid;
alter table category add cid int(3) not null first;
alter table category modify column cid int( 3 ) not null auto_increment,add primary key(cid);
select * from category  order by cid  ;

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