oracle基本操作，自己亲手做过了(二)
RENAME users1 TO users;--修改表名
COMMENT ON TABLE users IS '存放雇员信息';--表名的注释
COMMENT ON TABLE users.username IS '描述雇员姓名';--表中属性的注释
select * from users1 --查询表的所有属性
delete from users1 where userid=1;--删除表中的值
ALTER TABLE users1 ADD birhtday number(4);--增加表属性
ALTER TABLE users1 ADD pass NUMBER(4);
ALTER TABLE users1 DROP COLUMN username;--删除表属性
ALTER TABLE users1 MODIFY(col1 VARHCAR2(50), col2 VARCHAR2(100));--修改表属性 col1改为col2
drop table users1;--删除表结构
delete from users1 where username='二';--删除
SELECT min(userid) FROM users1;-- 查询学号最小的
update users set username='tianweichang', pwd='888888' where userid=2;
create sequence userid1;
insert into users values(userid1.nextval,'wangwu','55555');---插入
--创建视图
CREATE OR REPLACE VIEW usersView
AS
SELECT u.USERID,u.username
FROM users u JOIN users1 ON u.userid=users1.userid
WITH READ ONLY
select * from usersView --查询视图
--创建索引
CREATE UNIQUE INDEX UQ_ENAME_IDX ON users1(username);