oracle 基础知识

 

示例：

--id自增语法
CREATE SEQUENCE sequence  //创建序列名称
       [INCREMENT BY n]  //递增的序列值是n 如果n是正数就递增,如果是负数就递减 默认是1
       [START WITH n]    //开始的值,递增默认是minvalue 递减是maxvalue
       [{MAXVALUE n | NOMAXVALUE}] //最大值
       [{MINVALUE n | NOMINVALUE}] //最小值
       [{CYCLE | NOCYCLE}] //循环/不循环
       [{CACHE n | NOCACHE}];//分配并存入到内存中


--创建id 自增
create sequence seq_on_test 
increment by 1 
start with 1 
nomaxvalue 
nocycle 
nocache; 


--seq的两个方法 :
select seq_on_test.currval from dual; 
select seq_on_test.nextval from dual;



--建个表
create table testuser(
       sno  integer,
       sname varchar2(9) not null,
       ssex  varchar2(3) not null,
       sbirthday date,
       sclass varchar2(5),
       constraint pk_testuser primary key(sno)
);
comment on column testuser.sno is '学号（主键）';
comment on column testuser.sname is '学生姓名';
comment on column testuser.ssex is '学生性别';
comment on column testuser.sbirthday is '学生出生年月日';
comment on column testuser.sclass is '学生所在班级';


--触发器添加

create or replace trigger testuser_insert_trigger
  before insert on testuser  
  for each row  
declare
  -- local variable here
begin  
 
  select seq_on_test.nextval into :new.sno from dual;
end testuser_insert_trigger;   

insert into testuser(sname,ssex,sbirthday,sclass) values('小乔','女',to_date('1977-09-01','yyyy-mm-dd'),95033);






--添加数据
insert into testuser(sno,sname,ssex,sbirthday,sclass) values(seq_on_test.nextval,'貂蝉','女',to_date('1977-09-01','yyyy-mm-dd'),95033);
insert into testuser(sno,sname,ssex,sbirthday,sclass) values(seq_on_test.nextval,'小乔','女',to_date('1977-09-01','yyyy-mm-dd'),95033);

update testuser set sno = '101' where sname = '貂蝉';

select * from testuser;

delete from testuser where sno = '2';