create table tb_student(  id         NUMBER(10)      not null,  createtime     DATE         not null,  constraint PK_tb_student primary key (id));comment on table "tb_student" is'學(xué)生表';comment on column "tb_student"."id" is'主鍵id';comment on column "tb_student"."createtime" is'創(chuàng)建時間';--創(chuàng)建序列create sequence seq_tb_studentminvalue 1nomaxvaluestart with 1increment by 1nocycle  --一直累加，不循環(huán)nocache; --創(chuàng)建觸發(fā)器，如果insert語句不指定ID自動插入增長值CREATE OR REPLACE TRIGGER tr_tb_student BEFORE INSERT ON tb_student FOR EACH ROW WHEN (new.id is null)beginselect seq_tb_student.nextval into:new.id from dual;end;