oracle的函数

select upper('ccc') from dual;
select lower('CCC') from dual;
第一个字母大写
select initcap('ggg') from dual;
链接字符串
select concat(concat(first_name,' '),last_name) from employees;
select first_name||' '||last_name from employees;
截取字符串ya
select substr('guoyafei',4,2) from dual;
返回字符串长度
select length('gggg') from dual;
查询字符串位置 返回c2在c1中的位置
c1为原字符串 c2为用要查找的字符串   从第n1个字符开始查 第n2个匹配的
select instr('guoyafeiyafeiyafei','ya',5,2) from dual;

INSTR('GUOYAFEIYAFEIYAFEI','YA',5,2)
------------------------------------
                  14
不写n1 n2 默认从头开始 第一个匹配的
select instr('guoyafeiyafeiyafei','ya') from dual;

INSTR('GUOYAFEIYAFEIYAFEI','YA')
--------------------------------
                   4
查询字符串
lpad(c1，n,c2)返回长度为n的字符串
若是n《c1 从左至右截取制定长度的字符串
若是n》c1  c2 is null 空格是从左至右补充c1字符长度
若是n》c1  c2 不为空 c2是从左至右补充c1字符长度
select lpad('guoyf',10),lpad('guoyf',10,'l') ,lpad('guoyf',3,'l') from dual;

LPAD('GUOY LPAD('GUOY LPA
---------- ---------- ---
     guoyf lllllguoyf guo

create table aa(str varchar2(2000));
insert into aa select lpad('shiwei',2000,'l') from dual;
insert into aa values(lpad('shiwei',2000,'l'));

rpad(c1，n,c2)返回长度为n的字符串
若是n《c1 从左至右截取制定长度的字符串
若是n》c1  c2 is null 空格是从右至左补充c1字符长度
若是n》c1  c2 不为空 c2是从右至左补充c1字符长度
select rpad('guoyf',10),rpad('guoyf',10,'l') ,rpad('guoyf',3,'l') from dual;

RPAD('GUOY RPAD('GUOY RPA
---------- ---------- ---
guoyf       guoyflllll guo


修剪字符串 不指定修剪的字符串则修剪空格
both 修剪两边
leading 修剪头
trailing 修剪尾
select trim(both 'g' from 'guoyafeig'),trim(leading 'g' from 'guoyafeig'),trim(trailing 'g' from 'guoyafeig') from dual;

TRIM(BO TRIM(LEA TRIM(TRA
------- -------- --------
uoyafei uoyafeig guoyafei

select trim(both  from '   guoyafeig   ')from dual;

TRIM(BOTH
---------
guoyafeig



用shiwei替换first_name 中的teven
SQL> select replace(first_name,'teven','shiwei') from employees where first_name='Steven';

REPLACE(FIRST_NAME,'TEVEN','SHIWEI')
--------------------------------------------------------------------------------
Sshiwei
Sshiwei

SQL> select replace(first_name,'teven') from employees where first_name='Steven';

REPLACE(FIRST_NAME,'
--------------------
S
S




数值函数
round四舍五入
trunc 截断函数 不四舍五入
 select round(23.56),round(23.35),round(23.45,1),round(23.45,-1),round(25.45,-1) from dual;

ROUND(23.56) ROUND(23.35) ROUND(23.45,1) ROUND(23.45,-1) ROUND(25.45,-1)
------------ ------------ -------------- --------------- ---------------
      24           23        23.5          20          30

SQL> select round(588,-2) from dual;

ROUND(588,-2)
-------------
      600


select trunc(56.67),trunc(56.67,1),trunc(56.67,-1) from dual;

TRUNC(56.67) TRUNC(56.67,1) TRUNC(56.67,-1)
------------ -------------- ---------------
      56           56.6         50
求余
select mod(5,2) ,mod(8,4),mod(11,-4),mod(-11,4),mod(-11,-4) from dual;

  MOD(5,2)   MOD(8,4) MOD(11,-4) MOD(-11,4) MOD(-11,-4)
---------- ---------- ---------- ---------- -----------
     1        0           3     -3         -3

日期函数
NEXT_DAY(date,n)
从date时间点开始，下一個星期n的日期
 星期日 = 1  星期一 = 2  星期二 = 3
 星期三 = 4  星期四 = 5  星期五 = 6  星期六 = 7
select sysdate ,next_day(sysdate,1) from dual;

SYSDATE    NEXT_DAY(S
---------- ----------
2014-04-06 2014-04-13

转化函数
to_char()
to_date()
to_number()
to_timestamp()






nvl(n1,n2) 若是n1不为空返回n1，为空就返回n2
select last_name, nvl(to_char(commission_pct),'ccc') from employees where last_name like 'B%';

LAST_NAME          NVL(TO_CHAR(COMMISSION_PCT),'CCC')
------------------------- ----------------------------------------
Baer              ccc
Baida              ccc
Banda              .1
Bates              .15
Bell              ccc
Bernstein          .25
Bissot              ccc
Bloom              .2
Bull              ccc

nvl2(n1,n2,n3)c1不为空， 则返回c2 ，若是c1为空， 则返回c3

select last_name,salary,nvl2(commission_pct,salary+salary*commission_pct,salary) income from  employees where last_name like 'B%';

LAST_NAME              SALARY     INCOME
------------------------- ---------- ----------
Baer                   10000      10000
Baida                2900       2900
Banda                6200       6820
Bates                7300       8395
Bell                4000       4000
Bernstein            9500      11875
Bissot                3300       3300
Bloom                   10000      12000
Bull                4100       4100





case....end语句"tz_salary" 别名
select last_name,job_id,salary, case job_id
when 'it_prog' then 1.10*salary
when 'st_clerk' then 1.15*salary
when 'sa_rep' then 1.20*salary
else salary
end "tz_salary" from employees;

select last_name,case
when salary > 10000 then 9000
when salary >3000 then salary
 else 3000
end "tz_salary" from employees;

decode语句 可与case...end语句转换
decode(expr,s1,h1,s2,h2,s3,h3,.....,default)
select last_name,job_id,salary,
decode('job_id','it_prog',1.10*salary,'st_clerk',1.15*salary,'sa_rep',1.20*salary,salary ) "tz_salary"
from employees;