oracle中数据类型及函数

1. 字符串类型及函数

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create table t_user3(
  id number,
  username char(20),
  password varchar2(20),
  stuno varchar2(20)
);
insert into t_user3 (id, useramne, password, stuno) values (1, 'user1001            ', '123456', '110');
------------------------------

字符类型分3种：char(n) varchar(n) varchar2(n)；
    char(n)固定长度字符串，假如长度不足n，右边空格补齐；
    varchar(n)可变长度字符串，假如长度不足n，右边不会补齐；
    varchar2(n)可变长度字符串，Oracle官方推荐使用，向后兼容性好；
char(n) VS varchar2(n)
    char(n)查询效率相对较高，varchar2(n)存储空间相对较小；
SQL> select length(userName) as charlength,length(password) as varchar2length from t_user3;

lpad() 向左补全字符串
SQL> select lpad(stuno,6,'0') from t_user3;

rpad() 向右补全字符串
SQL> select rpad(stuno,6,'0') from t_user3;

lower() 返回字符串小写
SQL> select lower(userName) from t_user3;

upper() 返回字符串大写
SQL> select upper(userName) from t_user3;

initcap() 单词首字符大写
SQL> select initcap(userName) from t_user3;

length() 返回字符串长度
SQL> select length(password) from t_user3;

substr() 截取字符串
SQL> select substr(userName,1,2) from t_user3;

instr() 获取字符串出现的位置
SQL> select instr(password,'23') from t_user3;
SQL> select instr(password,'23',2) from t_user3;
SQL> select instr(password,'23',2,1) from t_user3;

ltrim() 删除左侧空格
SQL> select ltrim(userName) from t_user3;

rtrim() 删除右侧空格
SQL> select rtrim(userName) from t_user3;

trim() 删除两侧空格
SQL> select trim(userName) from t_user3;

concat() 串联字符串
SQL> select concat(userName,password) from t_user3;

reverse() 反转字符串
SQL> select reverse(userName) from t_user3;

2. 数值类型及函数

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create table t_number(
  id number,
  n1 number(7,3),
  n2 number(5,-3)
);
insert into t_number(id,n1,n2) values (1, -123.456, 0);
insert into t_number(id,n1,n2) values (2, 23.4564, 0);
insert into t_number(id,n1,n2) values (3, 23.4564, 123456);
insert into t_number(id,n1,n2) values (4, 23.4564, 123789);
insert into t_number(id,n1,n2) values (5, 23.4567, 123789);
insert into t_number(id,n1,n2) values (6, 23.4564, 123789);
------------------------------

number是oracle中的数据类型: number(precision,scale);
precision，scale均可选；
precision代表精度，sacle代表小数位的位数;
precision 范围[1,38] scale 范围[-84,127];
举例：12345.678中precision是8;scale是3;

abs() 求绝对值
SQL> select abs(n1) from t_number;

round() 四舍五入
SQL> select round(n1,2) from t_number where id=1;

ceil() 向上取整
SQL> select ceil(n1) from t_number where id=2;

floor 向下取整
SQL> select floor(n1) from t_number where id=2;

mod()取模
SQL> select mod(5,3) from dual;

sign()正负性
SQL> select sign(n1) from t_number where id=1;

sqrt()求平方根
SQL> select sqrt(9) from dual;

power()求乘方
SQL> select power(2,3) from dual;

trunc()截取
SQL> select trunc(123.456,2) from dual;

to_char() 格式化数值
常见的字符匹配有 0、9、，、$、FM、L、C
SQL> select to_char(123.45,'0000.000') from dual;
SQL> select to_char(123.45,'9999.999') from dual;
SQL> select to_char(123123,'99,999,999.99') from dual;
SQL> select to_char(123123.3,'FM99,999,999.99') from dual;
SQL> select to_char(123123.3,'$99,999,999.99') from dual;
SQL> select to_char(123123.3,'L99,999,999.99') from dual;
SQL> select to_char(123123.3,'99,999,999.99C') from dual;

3. 日期类型及函数

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create table t_date(
  id number,
  d1 date,
  d2 timestamp(6)
);
insert into t_date values(1,sysdate,systimestamp);

alter table t_date add(d3 date);???
update t_date set d3=to_date('2016-12-20','YYYY-MM-DD') where id=1;
update t_date set d3=to_date('2016-12-20 18:31:34','YYYY-MM-DD HH24:MI:SS') where id=1;
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date和timestamp(时间戳)
date包含信息century(世纪信息) year年 month月 day日 hour小时 minute分钟 second秒
timestamp一般用于日期时间要求非常精确的情况，精确到毫秒级；

date类型的常用函数：
SQL> select sysdate from dual;
SQL> select systimestamp from dual;

add_months添加月份
SQL> select add_months(d1,2) from t_date where id=1;

last_day返回指定日期月份的最后一天
SQL> select last_day(d1) from t_date where id=1;

months_between返回两个日期的相差月数
SQL> select months_between(d1,d3) from t_date where id=1;

next_day返回特定日期之后的一周内的日期
SQL> select next_day(d1,2) from t_date where id=1;

trunc截取日期
SQL> select trunc(d1,'YYYY') from t_date where id=1;
SQL> select trunc(d1,'MM') from t_date where id=1;
SQL> select trunc(d1,'DD') from t_date where id=1;
SQL> select trunc(d1,'HH') from t_date where id=1;
SQL> select trunc(d1,'MI') from t_date where id=1;

extract返回日期的某个域
SQL> select extract(year from sysdate) from dual;
SQL> select extract(month from sysdate) from dual;
SQL> select extract(day from sysdate) from dual;
SQL> select extract(hour from systimestamp) from dual;
SQL> select extract(minute from systimestamp) from dual;
SQL> select extract(second from systimestamp) from dual;

to_char将日期转换成字符串
SQL> select to_char(d1,'YYYY-MM-DD') from t_date where id=1;
SQL> select to_char(d1,'YYYY-MM-DD HH24:MI:SS') from t_date where id=1;

4. 其他常用处理函数

max求最大值
SQL> select max(sal) from emp;

min求最小值
SQL> select min(sal) from emp;

avg求平均值
SQL> select avg(sal) from emp;

sum求和
SQL> select sum(sal) from emp;

count统计记录数
SQL> select count(ename) from emp;

nvl空值处理
SQL> select ename,nvl(sal,0) from emp;

rownum行号
SQL> select e.*, rownum from emp e;

oracle分页
SQL> select * from (select a.*,rownum rn from (select * from emp) A where rownum<=10) where rn>5;

oracle中的运算
SQL> select 2+1 from dual;
SQL> select 2-1 from dual;
SQL> select 2*1 from dual;
SQL> select 2/1 from dual;

条件判断式
between and范围查询
SQL> select * from emp where sal between 900 and 1500;
SQL> select * from emp where sal>=900 and sal<=1500;

in集合范围
SQL> select ename,hiredate from emp where ename in (select distinct ename from bonus);

like模糊查询
SQL> select * from emp where ename like '%M%';
SQL> select * from emp where ename like 'M%';
SQL> select * from emp where ename like '_M%';