The primary key id is reset after deleting data in MySQL
Create database
create database db1;
use db1;
create table user3(
id int primary key auto_increment,
username varchar(16) not null unique ,
password varchar(16) not null,
createDatetime date
);
insert into user3 (username,password,createDatetime) values
("张伟","pass1","2019-07-11"),("王伟","pass2","2019-07-11"),
("王芳","pass3","2019-07-12"),("李伟","pass4","2019-07-11"),
("王秀英","pass5","2019-07-12"),("李秀英","pass6","2019-07-11"),
("李娜","pass7","2019-07-10"),("张秀英","pass8","2019-07-10"),
("刘伟","pass9","2019-07-12"),("张敏","pass10","2019-07-10");
Create data table
use db1;
create table user3(
id int primary key auto_increment,
username varchar(16) not null unique ,
password varchar(16) not null,
createDatetime date
);
Add data to the data table
insert into user3 (username,password,createDatetime) values
("张伟","pass1","2019-07-11"),("王伟","pass2","2019-07-11"),
("王芳","pass3","2019-07-12"),("李伟","pass4","2019-07-11"),
("王秀英","pass5","2019-07-12"),("李秀英","pass6","2019-07-11"),
("李娜","pass7","2019-07-10"),("张秀英","pass8","2019-07-10"),
("刘伟","pass9","2019-07-12"),("张敏","pass10","2019-07-10");
Select the last row of data to delete and insert new data
delete from user3 where password="pass10";
insert into user3 (username,password,createDatetime) values
("张三","pass","2019-7-13"),("李四","pass52","2019-7-10")
At this time, it was found that the newly inserted data id failed to start from 10.
To achieve the id output in order, we need to initialize the id and reset it
alter table user3 drop id;
alter table user3 add id int not null primary key auto_increment first;
After running, we can find that id is output in sequence again