Oracle中sequence使用方法简述

Oracle中,当需要建立一个自增字段时,需要用到sequence。sequence也可以在mysql中使用,但是有些差别,日后再补充,先把Oracle中sequence的基本使用总结一下,方便日后查阅。

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。

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