表定义：
CREATE TABLE departments ( IDNUMBER(10) NOT NULL, DEscriptION VARCHAr2(50) NOT NULL);ALTER TABLE departments ADD ( ConSTRAINT dept_pk PRIMARY KEY (ID));CREATE SEQUENCE dept_seq START WITH 1;
触发定义：
CREATE OR REPLACe TRIGGER dept_bir BEFORE INSERT ON departments FOR EACH ROWBEGIN SELECT dept_seq.NEXTVAL INTO :new.id FROM dual;END;/
更新：
IDENTITY 列现在在Oracle 12c上可用：
create table t1 ( c1 NUMBER GENERATED by default on null as IDENTITY, c2 VARCHAr2(10) );
或指定起始值和增量值，也防止任何插入到标识列（GENERATED ALWAYS）中（同样，仅适用于Oracle 12c +）
create table t1 ( c1 NUMBER GENERATED ALWAYS as IDENTITY(START with 1 INCREMENT by 1), c2 VARCHAr2(10) );
另外，Oracle 12还允许使用序列作为默认值：
CREATE SEQUENCE dept_seq START WITH 1;CREATE TABLE departments ( IDNUMBER(10) DEFAULT dept_seq.nextval NOT NULL, DEscriptION VARCHAr2(50) NOT NULL);ALTER TABLE departments ADD ( ConSTRAINT dept_pk PRIMARY KEY (ID));
