Mysql实例深入Mysql,SqlServer,Oracle主键自动增长的设置详解

create table customers(id int auto_increment primary key not null, name varchar(15));
insert into customers(name) values("name1"),("name2");
select id from customers;

create table customers(id int identity(1,1) primary key not null, name varchar(15));
insert into customers(name) values('name1'),('name2');
select id from customers;

use TESTDB2
--step1:创建表
create table customers(
    id int identity primary key not null,
    name varchar(15)
);
--step2:执行插入操作
insert into customers(id,name) values(1,'name1');
--报错:An explicit value for the identity column in table 'customers' can only be specified when a column list is used and IDENTITY_INSERT is ON.
--step3:放开主键列的自增长
SET IDENTITY_INSERT customers ON;
--step4:插入两条记录,主键分别为1和3.插入成功
insert into customers(id,name) values(1,'name1');
insert into customers(id,name) values(3,'name1');
--step5:再次插入一个主键为2的记录.插入成功
insert into customers(id,name) values(2,'name1');
--step6：插入重复主键,
--报错：Violation of PRIMARY KEY constraint 'PK__customer__3213E83F00551192'. Cannot insert duplicate key in object 'dbo.customers'.
insert into customers(id,name) values(3,'name1');
--step7：关闭IDENTITY_INSERT
SET IDENTITY_INSERT customers OFF;

create sequence customer_id_seq increment by 2 start with 1

create table customers(id int primary key not null, name varchar(15));
insert into customers values(customer_id_seq.nextval, 'name1');
insert into customers values(customer_id_seq.nextval, 'name2');
select id from customers;

create or replace
trigger trg_customers before insert on customers for each row
begin
select CUSTOMER_ID_SEQ.nextval into :new.id from dual;
end;

insert into customers(name) values('test');