Oracle中 表空间，数字函数，日期函数，转换函数，同义词，反向键索引

grant create tablespace to sll------------------------create tablespace y2164tabspaceDATAFILE 'C:\app\linlin\oradata\orcl\y2164tabspace.dbf' size 10mAUTOEXTEND on next 32m maxsize unlimitedselect tablespace_name from user_tablespacescreate  tablespace y2164tabspace2DATAFILE 'C:\app\linlin\oradata\orcl\y2164tabspace2.dbf' size 10mcreate  tablespace y2164tabspace3DATAFILE 'C:\app\linlin\oradata\orcl\y2164tabspace3.dbf'  size 10m,'C:\app\linlin\oradata\orcl\y2164tabspace3-1.dbf' size 10m==========================================================----------字符函数select Lower('Abc') from dual;select upper('Abc') from dual;select initcap('abc') from dual;select concat('abc','end') from dual;select substr('Spring Boot实战',3)from dual;select substr('Spring Boot实战',3,8)from dual;select length('abc') from dual;select lengthb('中国人')from dual;select instr('Srpingboot springcloud',3,2) from dual;select instr('Srpingboot springcloud springmvc','ing',-3,2) from dual;select lpad('Happy',10,'*') from dual;select rpad('Happy1234522',10,'*') from dual;select trim('A      bv   ') from dual;select trim('a' from 'ahappya') from dual;--------日期函数select Months_Between(sysdate,"TO_DATE"('1998-09-24','yyyy-MM-dd'))from dual;select add_months(sysdate,1) from dual;---------------select userenv('language') from dual;select floor(sysdate-to_date('1998-09-24','yyyy-MM-dd')) from dual;select sysdate from dual;select to_char(sal,'L9,999.99') from emp;select round(12.45,3) from dual;select trunc(12.49,1) from dual;select sal+nvl(comm,0) from emp;select * from emp;select sal+nvl2(comm,comm*2,0) from emp;select ename,decode(deptno,10,'sales',20,'money',30,'yanfa','baojiebu') from emp;

--sys_guid函数select sys_guid()  from dual;-----------创建私有同义词create or replace synonym emp for employee;-----创建共有同义词create public synonym employee for scott.employeegrant select on employee to sll--以sll登录select * from employee----删除同义词（共有，私有）drop synonym emp;drop public synonym employee;------------------------------------------------在订单表中国年，只允许当前员工查看自己的订单记录--当前用户 scott--获取create view权限create or replace view v_myordersas select * from orderswhere sales req id=(select empno from employeewhere ename=(select user from dual));select  * from  v_myordersselect  * from  dept;----------------------------------在员工表中，普通职员只允许看姓名和部门列-----------create or replace view v_employeeas select empno,ename,e.deptno,dname from employee einner join dept d on e.deptno=d.deptno-------------------------------------------------------------索引---------------------------------------反向键索引create unique index idx_empno on employee(empno) reversealter table employee add constraint PK_empnoprimary key(empno)using index idx_empnoselect * from employee where empno=7900