Oracle学习笔记(四)

一、控制用户存取 
1、创建修改用户Creating Users 
Create/alter user new_user identified by password; 
例：create user user_1 indentified by pwd_1 
alter user user_1 identified by pwd_2 
2、给用户授予权限 
grant privilege[,privilege] to user [,user|role,public...] 
一些系统权限： 
create session/table/sequence/view/procedure 

alter/delete/execute/index/insert/references/select/update 
grant object_priv [(columns)] 
on object 
to {user|role|public} 
[with grant option] 
例如: 
给用户user_1授予查询tt1表的权限 
grant select on tt1表 to user_1 
给用户user_1授予修改“表1”中(列1，列2)的权限 
grant update(列1，列2) on 表1 to user_1; 
给用户user_1 授予查询权限并可以把该权限授予其他用户的权限 
grant select 
on tt1表 
to user_1 
with grant option 
把权限授予所有用户 
grant select 
on 表1 
to public; 

给用户user_1授权 
grant create session to user_1; 

二、创建角色并给角色授权 
1、创建角色 
create role mangager; 
例如：create role test_role1; 
2、给角色授权 
grant create table,create view to manager; 
例如：grant create table to test_role1; 

3、把角色授予用户 
grant manager to user_1,user_2... 
grant test_user1 to user_1; 

三、取消用户权限 
revoke {privilege [,privilege...]|all} 
on object 
from {user[,user...]|role|public} 
[cascade constraints]; 

revoke select on 表1 from user_1; 

四、Database Links 
create public database link hq.acme.com using 'sales'; 
select * from emp@hq.acme.com; 

五、 oracle取并集、交集、差集 
所取的列的数据类型必须兼容 
1、取并集 
union ：会对数据排序，重复记录压缩，union all不会 
select employee_id,job_id from employess 
union 
select employee_id,job_id from job_history; 
取所有并集不去除重复数据 
select employee_id,job_id from employess 
union all 
select employee_id,job_id from job_history; 

2、取交集 
select employee_id,job_id from employess 
intersect 
select employee_id,job_id from job_history; 

3、差集 
表employess去掉共同拥有的数据 
select employee_id,job_id from employess 
minus 
select employee_id,job_id from job_history; 

六、日期时间函数 
求时差 
select tz_offset('US/Eastern') from dual; 

alter session set time_zone='-8:0'; 
select sessiontimezone,current_date from dual; 
alter session set time_zone='-8:0'; 
select sessiontimezone,current_timestamp from dual; 

alter session set time_zone='-8:0'; 
select current_timestamp,localtimestamp from dual; 

select dbtimezone,sessiontimezone from dual; 
select from_tz(timestamp'2000-03-23 08:00:00','3:00') from dual; 

select to_timestamp('2000-02-01 11:00:00','YYYY-MM-DD HH:MI:SS')from dual; 

select to_timestamp_tz('2000-02-01 11:00:00','YYYY-MM-DD HH:MI:SS TZH:TZM')from dual; 
to_ymininterval()