oracle通过序列来实现主键的自增

建表语句：

CREATE TABLE tb_user(       ID VARCHAR2(20) PRIMARY KEY,       NAME VARCHAR2(20));

创建序列：

CREATE SEQUENCE seq_tb_user       START WITH 1       INCREMENT BY 1;

创建触发器：

CREATE OR REPLACE TRIGGER TG_TB_USER  BEFORE INSERT ON TB_USER  FOR EACH ROWBEGIN  SELECT SEQ_TB_USER.NEXTVAL INTO :NEW.ID FROM DUAL;END;

测试：

INSERT INTO TB_USER (NAME) VALUES ('yyb');

SELECT * FROM TB_USER;