我們常常在表中需要插入一些自動增長的值;

一方面,我們可以手動新增這些值，

另一方面,oracle提供的sequence可以幫助我們實現插入的值自動增長,

而不需要我們手動的提供值,我們需要做的就是設定好sequence的初值和增長值即可。

關於序列的定義和引數設定,

下面是一個例項：

create table goods( goods_id varchar2(5) primary key, goods_name varchar2(20), store_date date, goods_num number(5)); create sequence seq_goods_id start with 10001 increment by 1 nomaxvalue nocycle nocache order;

1.在insert語句中,直接使用sequence.nextval引用；

insert into goods(goods_id,goods_name,store_date,goods_num) values(seq_goods_id.nextval,'聖爽礦泉水',to_date('2011-01-01','yyyy-mm-dd'),500); insert into goods(goods_id,goods_name,store_date,goods_num) values(seq_goods_id.nextval,'海飛絲男士',to_date('2011-01-08','yyyy-mm-dd'),1000); insert into goods(goods_id,goods_name,store_date,goods_num) values(seq_goods_id.nextval,'洽洽瓜子',to_date('2011-02-25','yyyy-mm-dd'),950); SQL> select * from goods; GOODS_ID GOODS_NAME STORE_DATE GOODS_NUM -------- -------------------- ----------- --------- 10001 聖爽礦泉水 2011-1-1 500 10002 海飛絲男士 2011-1-8 1000 10003 洽洽瓜子 2011-2-25 950

注意：在首次引用定義好的sequence時,必須先引用nextval,否則你會得到下面的錯誤：

SQL> create sequence ddd 2 start with 1 3 increment by 1 4 nomaxvalue; Sequence created SQL> select ddd.currval from dual; select ddd.currval from dual ORA-08002: sequence DDD.CURRVAL is not yet defined in this session SQL> select ddd.nextval from dual; NEXTVAL ---------- 1

2.通過before insert觸發器

每一次向表中新增值時,都觸動此觸發器,自動為這個insert語句加上一個sequence值.

create or replace trigger tri_goods_id before insert on goods for each row begin select seq_goods_id.nextval into :new.goods_id from dual; end tri_goods_id; insert into goods(goods_name,store_date,goods_num) values('銀鷺八寶粥',to_date('2011-03-26','yyyy-mm-dd'),100); insert into goods(goods_name,store_date,goods_num) values('茅臺啤酒',to_date('2011-02-10','yyyy-mm-dd'),10000); SQL> select * from goods; GOODS_ID GOODS_NAME STORE_DATE GOODS_NUM -------- -------------------- ----------- --------- 10001 聖爽礦泉水 2011-1-1 500 10002 海飛絲男士 2011-1-8 1000 10003 洽洽瓜子 2011-2-25 950 10004 銀鷺八寶粥 2011-3-26 100 10005 茅臺啤酒 2011-2-10 10000 

sequence有兩個偽列:currval和nextval.

currval:引用當前的sequence值，

nextval:引用下一個sequence值.

那麼currval和nextval可以引用在那些場合呢？那些場合又不適合用此二值呢？

You can use CURRVAL and NEXTVAL in: 1.The SELECT list of a SELECT statement that is not contained in a subquery, materialized view, or view 2.The SELECT list of a subquery in an INSERT statement 3.The VALUES clause of an INSERT statement 4.The SET clause of an UPDATE statement You cannot use CURRVAL and NEXTVAL: 1.A subquery in a DELETE, SELECT, or UPDATE statement 2.A query of a view or of a materialized view 3.A SELECT statement with the DISTINCT operator Pseudocolumns 4.A SELECT statement with a GROUP BY clause or ORDER BY clause 5.A SELECT statement that is combined with another SELECT statement with the UNION, INTERSECT, or MINUS set operator 6.The WHERE clause of a SELECT statement 7.DEFAULT value of a column in a CREATE TABLE or ALTER TABLE statement 8.The condition of a CHECK constraint