mysql-12序列使用

mysql序列是一组整数：1，2，3....，由于一张数据表只能有一个字段自增主键，如果你想实现其他字段自动增加，就可以使用mysql序列来实现。

使用auto_increment来定义列

drop table if EXISTS test_autoincrement ;
create table `test_autoincrement`(
    `id` int UNSIGNED not null auto_increment,
    PRIMARY KEY (id),
    `name` varchar(20) not null,
    `date` date not null,
    `origin` varchar(30)
    );
insert into test_autoincrement (name,date,origin) values
    ('housefly','2001-09-10','kitchen');
-- 使用last_insert_id() 可以查看当前操作的次数
select LAST_INSERT_ID();
select * from test_autoincrement;
insert into test_autoincrement values
    (null,"millipede",'2001-09-10','driverway'),
    (null,"grasshopper",'2001-09-10','front yard');
-- 即便插入多行，也只显示插入第一行时产生的值
select LAST_INSERT_ID();
select * from test_autoincrement;

重置序列

先删除列，再添加列

drop table if EXISTS test_autoincrement ;
create table `test_autoincrement`(
    `id` int UNSIGNED not null auto_increment,
    PRIMARY KEY (id),
    `name` varchar(20) not null,
    `date` date not null,
    `origin` varchar(30)
    );
insert into test_autoincrement (name,date,origin) values
    ('housefly','2001-09-10','kitchen'),
    ("millipede",'2001-09-10','driverway'),
    ("grasshopper",'2001-09-10','front yard');
alter table test_autoincrement drop id;
select * from test_autoincrement;
alter table test_autoincrement add id int(3) UNSIGNED not null auto_increment FIRST,
    add primary key (id);
select * from test_autoincrement;

设置序列的开始值

建表时设置序列值

create table `test_autoincrement` 
    (`id` int(3) UNSIGNED not null auto_increment,
    primary key (id),
    `name` varchar(20) not null )
    engine=innodb auto_increment=100 charset=utf8;
insert into test_autoincrement values
    (null,"tom"),
    (null,"jerry");
select * from test_autoincrement;