Oracle中sequence使用方法简述

1、创建sequence：

create sequence SEQ_ON_USER
minvalue 1
maxvalue 999999999999999999999999999
start with 1
increment by 1
nocache; 

说明：

minvalue：序列最小值

maxvalue/nomaxvalue：序列最大值/没有最大值

start with 1：序列从1开始

increment by 1：每次增加1

cache/nocache：nocache不缓存。cache缓存。开启缓存，效率高，只是如果数据库宕机了，缓存丢失，会出现序列跳号情况。

2、查看已有sequence：

select * from user_sequences; 
select * from user_sequences;

3、删除指定sequence：

DROP SEQUENCE SEQ_ON_USER； 
DROP SEQUENCE SEQ_ON_USER；

4、查看指定sequence的当前值：

两种方式：

select last_number from user_sequences wheresequence_name='SEQ_ON_USER'; 
select last_number from user_sequences wheresequence_name='SEQ_ON_USER';

select SEQ_ON_USER.nextval from sys.dual; 
select SEQ_ON_USER.nextval from sys.dual; 

5、创建触发器使用sequence设置主键自动插入。

create or replace trigger "SEQ_ON_USER_GENERATOR" before 
  insert on databasename1.T_USER for each row 
  declare 
        mid number, 
  begin 
    select SEQ_ON_USER.nextval into mid from dual; 
    :new.id:=mid; 
  end 
 
create trigger SEQ_ON_USER_Trigger 
 
before insert on T_USER for each row 
begin 
select SEQ_ON_USER.nextval into :new.id from dual; 
end SEQ_ON_USER_Trigger; 
create or replace trigger "SEQ_ON_USER_GENERATOR" before
  insert on databasename1.T_USER for each row
  declare
        mid number,
  begin
    select SEQ_ON_USER.nextval into mid from dual;
    :new.id:=mid;
  end

create trigger SEQ_ON_USER_Trigger

before insert on T_USER for each row
begin
select SEQ_ON_USER.nextval into :new.id from dual;
end SEQ_ON_USER_Trigger;

6、代码中使用sequence.nextval插入主键值。