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'學生表';comment on column "tb_student"."id" is'主鍵id';comment on column "tb_student"."createtime" is'創建時間';--創建序列create sequence seq_tb_studentminvalue 1nomaxvaluestart with 1increment by 1nocycle   --一直累加，不循環--nocache;  --不緩存cache 10; --緩存10條--創建觸發器，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;
//其他方法
法一：
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create table tb_student(   id                 integer generated by default as identity                      not null constraint PK_tb_student primary key,   createtime         DATE                 not NULL);
法二：
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--創建序列create sequence seq_tb_studentminvalue 1nomaxvaluestart with 1increment by 1nocycle   --一直累加，不循環nocache;  create table tb_student(   id                  integer default seq_tb_student.nextval                       not null constraint PK_tb_student primary key,   createtime         DATE                 not NULL);