Oracle初步

--创建用户
create user qjt identified by 1234

--权限
grant connect to qjt

grant resource to qjt

--建表
create table userinfo
(id number primary key not null)

--查询有几张表
select * from all_tables where owner=‘QJT‘

--伪列
select id,rowid,rownum from userinfo

--查询自然排序的第三条记录
select * from
(
select ename,rownum rn from emp
) temp
where rn=3

--查询教师表中薪水排名第五的教师信息
select * from 
(
select rownum rn,ta.* from
( 
select ename,sal,rownum rn from emp order by sal desc
)ta where rownum<6
)where rn>=5

--分页
--方法一
select * from
(
select temp.*,rownum rn from 
(
select emp.* from emp
order by sal desc
) temp
where rownum<=9
)
where rn>=5
--方法二
select * from 
(
SELECT temp.*,ROWNUM rn FROM
(
SELECT * FROM emp e ORDER BY e.sal DESC
)temp
)temp2
WHERE TEMP2.rn BETWEEN 5 AND 9

--授权
grant select on HAPPYY2165.STUDENT to scott

--解锁用户
alter user hr account unlock

--收回权限
revoke select on qjt from SCOTT

--通过角色控制
--自定义角色
CREATE role role_testy2165

--将查询表的权限和角色绑定
grant SELECT ON Y2165."student" TO role_testy2165

--给用户分配角色
GRANT role_testy2165 to SCOTT

--distinct查询不重复的数据
select DISTINCT "stuname","stuage" from STUDENT;

--创建学生表的备份表
create table studentbak
as
select * from STUDENT

--删除相同的列，保留id最大的
DELETE FROM student
WHERE "stuno" NOT IN(SELECT "MAX"("stuno") FROM student GROUP BY "stuname","stuage")

SELECT 1+1 FROM dual

SELECT ‘你‘||‘好‘ FROM dual

SELECT ‘运算结果‘||‘5‘ FROM dual

--交集
SELECT deptno FROM dept
INTERSECT 
SELECT DISTINCT deptno FROM emp

--减集
SELECT deptno FROM dept
MINUS 
SELECT DISTINCT deptno FROM emp