Oracle函数

  --length(‘字符串‘)：字符个数统计
   -- lengthb(‘字符串‘)：字节个数统计
select length(‘呵呵‘) 字符数，lengthb(‘呵呵‘) as 字节数 from dual;

--instr(‘大字符串‘,‘小字符串‘)返回小字符串在大字符串中出现的位置
select instr(‘happy hehe‘,‘he‘,2,2) "Instring" from dual;

select instr(‘happy hehe‘,‘he‘,-2,2) "Reversed Instring" from dual;

select instr(‘happy hehe‘,‘he‘,2,2) "Instring in bytes" from dual;

--lpad()和rpad()
select lpad(‘happy‘,10,‘*‘) from dual;

select MONTHS_BETWEEN
(TO_DATE(‘02-02-1995‘,‘MM-DD-YYYY‘),
TO_DATE(‘01-01-1995‘,‘MM-DD-YYYY‘)) "Months"
from dual;

--向指定日期中加上若干月数
select TO_CHAR(ADD_MONTHS(hiredate,1),‘DD-MON-YYYY‘) "Next month" 
from emp
where ENAME=‘JONES‘;

--两个日期间的天数
select floor(sysdate-to_date(‘20020405‘,‘yyyymmdd‘)) from dual;

--转换函数
--隐式函数
select * from emp
where hiredate=‘17-12月-80‘;

--显式函数
   --01.to_char()对日期的转换
   select to_char(sysdate,‘yyyy-mm-dd hh24:mi:ss‘) from dual;

--02.to_char()对数字的转换
   select to_char(sal,‘L9,999.99‘) 
   from emp;

--数字函数
  --01.Round()四舍五入
  select round(12.45,1) from dual;

 --02.trunc()截断
  select trunc(15.19,1) "Truncate" from dual;

select sal*12工资,comm 奖金,sal*12+nvl(comm,0) from emp;

select sal*12工资,comm 奖金,sal*12+nvl2(comm,comm,0) from emp;

--decode函数
  select ename,empno,
      decode (ename,‘SMITH‘,1,
      ‘ALLEN‘,2,
      ‘WARD‘,3,
      ‘JONES‘,4) "Location"
      from emp
      where empno<7600
      order by empno,"Location"