MySQL

Question

查询创建表格：

create table if not exists person ( 
roll_no int(4) AUTO_INCREMENT primary key,
name varchar(25),  
city varchar(25));

查询设置自动增量主键的起始编号：

  

alter table person auto_increment = 1;

查询以插入数据：

insert into person (name,city) values("Maxwell", "Pune");
insert into person (name,city) values("Baldwin", "Bengaluru");
insert into person (name,city) values("Novartis", "Paris");
insert into person (name,city) values("Shaun", "Mumbai");
insert into person (name,city) values("Beckham", "Toronto");
insert into person (name,city) values("Ashish", "Bengaluru");
insert into person (name,city) values("David", "Paris");
insert into person (name,city) values("PK", "London");
insert into person (name,city) values("Chris", "Bengaluru");
insert into person (name,city) values("Aston", "Mumbai");

查询删除行：

  

delete from person where roll_no=5;

删除行后的表格结构：

roll_no      name       city
1            Maxwell    Pune
2            Baldwin    Bengaluru
3            Novartis   Paris
4            Shaun      Mumbai
6            Ashish     Bengaluru
7            David      Paris
8            PK         London
9            Chris      Bengaluru
10           Aston      Mumbai

现在，在寻找恢复已删除行的同时，编译器 <错误 “Duplicate entry '5' for key 'PRIMARY'”

用于重新设置已删除行的查询。

update person set roll_no = roll_no + 1 where roll_no >=4 order by roll_no desc;
insert into person (roll_no, name, city) VALUES (5, "Beckham", "Toronto");

这个问题的可能原因是什么？ 强烈建议任何输入。

Answer 1

如此简单，在您的更新查询中，您将4变为5，然后尝试插入5.这就是它重复的原因。

Answer 2

要恢复已删除的行，只需执行insert语句。可以简单地删除update语句并使用以下命令：

<强>查询

insert into person (roll_no, name, city) VALUES (5, "Beckham", "Toronto");