select * from scott.emp;
select ename "name"from scott.emp;
--lower转化小写的用法
select lower(ename) ename ,sal from scott.emp;

select * from scott.emp where lower(ename)=‘allen‘;
--upper 转化大写
select upper(ename) "ename" from scott.emp ;
--INITCAP 首字母大写
select INITCAP(ename) as ename from scott.emp ;
--CONCAT 或 ||连接
select concat(ename,sal )from scott.emp;
select concat (‘wang‘,‘feng‘) ename from scott.emp;
select ename||‘  ‘||sal  ename from scott.emp;
select ‘@‘||ename||‘@‘as ename from scott.emp;
--SUBSTR
select SUBSTR(ename ,1,3)from scott.emp;
select substr(hiredate , 0)from scott.emp;
--寻找月份
select* from scott.emp where hiredate = ‘22-2月-81‘;
select* from scott.emp where hiredate > ‘1-1月-81‘;
select * from scott.emp where hiredate between ‘1-1月-81‘and‘31-12月- 81‘;
--LENGTH 长度
select length(ename) as chang from scott.emp;
--INSTR返回第一次出现某字符的位置
select INSTR(ename,‘L‘)from scott.emp;
--LPAd 变成一个长度为10的字符，不够用*代替
select lpad (ename ,10,‘*‘)FROM scott.emp;
--RPAD 变成一个长度为10的字符串，不够在其后面加*
select rpad (ename ,10,‘*‘)from scott.emp;
select rpad (ename ,3)from scott.emp;
--TRIM 去除字符两端的某个字符
select trim (‘C‘from ename)from scott.emp;
select ‘[‘||‘    ‘||ename||‘   ‘||‘]‘from scott.emp;
select trim (ename)from (select ‘    [‘||‘    ‘||ename||‘   ‘||‘]    ‘ ename from scott.emp);
select trim (‘a‘from ‘aaabbbbaa‘) from scott.emp;
--"Contains ‘a‘?"
--select from scott.emp;
--ROUND: 四舍五入
select round(7850.3854512145,5)from scott.emp;
select round(7850.38,5)from scott.emp;
select round(7850.38,-2)from scott.emp;
--TRUNC:     截断
select trunc (222222.2222,2)from scott.emp ;
select trunc (222222,-2)from scott.emp ;
--日期报错select trunc (hiredate)from scott.emp;
select trunc (222222.222,0)from scott.emp ;
--MOD: 求余
select mod (3,2)from scott.emp;
--sysdate 返回时间毫秒表示
select sysdate-hiredate  from scott.emp;
--substr负数从后面算起
Select substr(‘abcde‘,-4,3) from scott.emp;
--replace 
select replace (ename,‘A‘,‘a‘)from scott.emp;
--Months_between()
select months_between(sysdate,add_months(sysdate,-2)) from scott.emp;
select sysdate from scott.emp;--返回现在时间
--add_months
select add_months(sysdate,1) from scott.emp;
--select add_days(sysdate,2)from scott.emp;              add-years (),add_day()无效
--next_day
select next_day(sysdate,‘星期一‘)from scott.emp;
--order by
select * from scott.emp  order by sal,empno asc;
select * from scott.emp  order by sal,empno desc;
--Last_day
select last_day (sysdate)from scott.emp;
select add_months (sysdate,-2) from scott.emp;

--ROUND 日期
select round (sysdate,‘year‘)from scott.emp; 
select round (sysdate ,‘month‘)from scott.emp;
select round (sysdate,‘day‘)from scott.emp;
--trunc截取日期
select trunc (sysdate,‘year‘)from scott.emp;
select trunc (sysdate,‘month‘)from scott.emp;
select trunc (sysdate,‘day‘)from dual;
--转化函数
-- to_char()对于日期的转化
select to_char (sysdate,‘yyyy‘)from scott.emp;
select to_char (hiredate,‘yy‘)from scott.emp;
select to_char (sysdate ,‘yyyy-mm-dd‘)from scott.emp;
select to_char (hiredate, ‘mm‘)from scott.emp;
--生日在5到8月之间
select *from scott.emp where to_number(to_char (hiredate, ‘mm‘))between 7 and 9;
select *from scott.emp where to_number(to_char (hiredate, ‘mmdd‘))between to_number(to_char (sysdate, ‘mmdd‘)) and  to_number(to_char (add_months(sysdate,2), ‘mmdd‘)); 
select to_number(to_char (add_months(sysdate,2), ‘mm‘)) from dual;
select to_char(sysdate,‘fmyyyy-mm-dd‘) from scott.emp;
select to_char (hiredate,‘fmyyyy-mm‘) from scott.emp;
select to_char (sysdate,‘fmyyyy-mm-dd-hh24-mi-ss‘)from scott.emp;
select to_char (sysdate,‘fmyyyy/mm/dd/hh/mi/ss‘)from scott.emp;
select to_char(sal,‘l999,999‘) from scott.emp;
select to_char(sal,‘$999,999‘) from scott.emp;
select to_char (sysdate,‘d‘)from Scott.emp;
--To_number把字符串变成数字
select to_number(‘13‘)+to_number(‘14‘) from dual;
--to_date
select to_date (‘20090222‘,‘yyyymmdd‘)from dual;
--NVL()函数
select nvl(comm,0) from scott.emp;
select * from scott.emp;
--nvl2(comm, sal+comm, sal)
select nvl2(comm, sal+comm, sal) from scott.emp;
--COALESCE()函数
select empno, ename, sal, comm, coalesce(sal+comm, sal, 0)as sal from scott.emp;
--case
select empno, ename, sal, case
deptno
when 10 then ‘财务部‘ when
20 then ‘研发部‘ when 30
then ‘销售部‘
else ‘未知部门‘
end 
from scott.emp;
--DECODE()函数
select empno, ename, sal, decode(deptno,
10, ‘财务部‘, 
20, ‘研发部‘,
30, ‘销售部‘, ‘未知
部门‘) 部门
from scott.emp;
select * from scott.emp where job != ‘CLERK‘;

select * from scott.emp  order by sal desc ;
--查询出每个部门的编号、名称、位置、部门人数、平均工资
select * from scott.emp where deptno = 10;