OracleOracle常用函数

select * from scott.dept;
select * from scott.emp;

–dual 是 Oracle提供的一个虚表
select length(‘hello’) from dual;

–常用函数
–lower把大写转小写 upper把小写转大写
select * from scott.emp where ename=’smith’;
–搜索字母转为小写后的结果
select * from scott.emp where lower(ename)=’smith’;

select upper(‘helloworld’) from dual;
select lower(‘HELLOWORLD’) from dual;

–INITCAP使串中的所有单词的首字母变为题写
select initcap(‘sql course’) from dual;

–CONCAT 连接三个字符串
select concat(‘Hello’,’World’) from dual;

–substr 取子字符串,从start先河,取count个
select substr(‘HelloWorld’,1,5) from dual;

–substr 取子字符串,从4开端取到末尾
select substr(‘HelloWorld’,-4) from dual;

–LENGTH 重返字符串的长短
select length(‘HelloWorld’) from dual;

–INSTR(string,char)
在一个字符串中寻找指定的字符,重临发现指定的字符的地点,从1起来
select instr(‘HelloWorld’,’o’) from dual;

–RPAD在列的左边粘贴字符,LPAD在列的右边粘贴字符
select rpad(sal,8,’*’) from scott.emp;

select lpad(sal,8,’*’) from scott.emp;

–TRIM删除首尾的空字符串
select trim(‘ HelloWorld ‘) from dual;
select length(‘ HelloWorld ‘) from dual;
select length(trim(‘ HelloWorld ‘)) from dual;

–TRIM删除首尾的H(对大小写敏感)
select trim(‘H’ from ‘HelloWorldH’) from dual;

–TRIM删除首的H
select trim(leading ‘H’ from ‘HelloWorldH’) from dual;

–TRIM删除尾的H
select trim(trailing ‘H’ from ‘HelloWorldH’) from dual;

–TRIM删除首尾的H
select trim(both ‘H’ from ‘HelloWorldH’) from dual;

–REPLACE(‘string’,’s1′,’s2′)
–string 希望被沟通的字符或变量
–s1 需要被交换的字符串 s2 替换的字符串
select replace(‘HelloWorldH’,’ll’,’FF’) from dual;

–数值函数 Round四舍五入
select Round(3.14159,3) from dual;

–TRUNC截断
select TRUNC(3.14159,3) from dual;

–取模
select MOD(1600,300) from dual;

–日期函数

create table tb_test(
currdate date
);

select * from tb_test;

–查询系统时间
select sysdate from dual;

–插入sysdate
insert into tb_test(currdate)values(sysdate);
–to_date将自定义日期格式字符串插入date类型的数码
insert into tb_test(currdate)values(to_date(‘2018/1/14
02:03:42′,’yyyy/mm/dd hh:mi:ss’));
insert into
tb_test(currdate)values(to_date(‘2018/1/14′,’yyyy/mm/dd’));
–日期函数
–oracle的日期类型时date 默认是yyyy/mm/dd hh:mi:ss
select sysdate from dual;

–在日期上添加或减去一个数字结果仍为日期
select sysdate+84 from dual;

–多个转移函数 to_date to_char to_number
–to_date(日期字符串,格式)
select to_date(‘2018/1/14 02:03:42′,’yyyy/mm/dd hh:mi:ss’) from dual;
select to_date(‘2018/1/14′,’yyyy/mm/dd’) from dual;

–to_char(日期,格式) 将日期转成字符
select to_char(sysdate,’yyyy/mm/dd’) from dual;
select to_char(sysdate,’yyyy/mm/dd hh:mi:ss’) from dual;
select to_char(sysdate,’mm’) from dual;
–将数字转成字符
select to_char(3.14159) from dual;

–to_number(字符串) 将一个字符串的数字转成number类型
select to_number(‘123.123’) from dual;
–无法将非数字的字符串转成number类型
select tb_number(‘abc’) from dual;

–六个日子相减再次来到日期之间距离的气数
select to_date(‘2018/04/08′,’yyyy/mm/dd’)-sysdate from dual;
select TRUNC(to_date(‘2018/04/08′,’yyyy/mm/dd’)-sysdate,0) from dual;
select sysdate-to_date(‘2018/04/08′,’yyyy/mm/dd’) from dual;

–可以用数字除24来向日期中增长或减去刻钟
select sysdate+2/24 from dual;
–可以用数字除24再除60向日期中加上分钟
select sysdate+2/24/60 from dual;

–再次回到d1,d2之间月的数码,d1,d2可为字符串
select months_between(
to_date(‘2018-04-08′,’yyyy-mm-dd’),
to_date(‘2017-11-20′,’yyyy-mm-dd’)
)as months from dual;

–再次回到日期d加上3个月后的日子,3是整数
select add_months(sysdate,3) from dual;

–再次来到日期d后率先个星期几的日子
select next_day(sysdate,’星期二’) from dual;
–外国周五是1 , 所以3指礼拜六
select next_day(sysdate,3) from dual;

–重回d所在月最终一天的日子
select last_day(sysdate) from dual;

–得到下一钟头 0分0秒
select trunc(sysdate+1/24,’hh’) from dual;

–拿到下一天 0分0秒
select trunc(sysdate+1,’dd’) from dual;

–拿到下9月 1号0分0秒
select last_day(sysdate) from dual;
select trunc(last_day(sysdate)+1) from dual;

–得到下一年 12月1号0分0秒
select trunc(sysdate,’yyyy’) from dual;
select add_months(trunc(sysdate,’yyyy’),12) from dual;

–Round四舍五入函数 默认遵照 dd举办 4舍5入 领先中午 12点就进来下一天
select Round(sysdate) from dual;

–领先15号重返下一个月
select Round(sysdate,’mm’) from dual;
–超越9月就回来下一年十月1号
select Round(sysdate,’yyyy’) from dual;

–截断日期
select trunc(sysdate,’mm’) from dual;
select trunc(sysdate,’dd’) from dual;
select trunc(sysdate,’hh’) from dual;

–定时器
–每分钟实施
select trunc(sysdate,’mi’)+1/24/60 from dual;

–每一天定时执行3
–例如:每一天的黎明2点执行
select trunc(sysdate)+1+2/24 from dual;

–周周定时实施
–例如:每一周一黎明2点实施
select trunc(next_day(sysdate,2))+2/24 from dual;

–每月定时进行
–例如:每月1日凌晨2点执行
select trunc(last_day(sysdate))+1+2/24 from dual;

–每季度定时执行
–例如每季度的首先天凌晨2点执行
select trunc(add_months(sysdate,3),’Q’)+2/24 from dual;

–每半年定时实施
–例如:每年7月1日和1月1日凌晨2点
select add_months(trunc(sysdate,’yyyy’),6)+2/24 from dual;

–每年定时执行
–例如:每年12月1日和凌晨2点推行
select add_months(trunc(sysdate,’yyyy’),12)+2/24 from dual;

–通用函数完成部分意义
–nvl函数 假如第一个参数为null,则取第二个参数
select comm from scott.emp;
select nvl(comm,0) from scott.emp;

–使用0替换null的comm,统计年收入
select ename,sal,comm,(sal+comm)*12 年收入 from scott.emp;
select ename,sal,nvl(comm,0),(sal+nvl(comm,0))*12 from scott.emp;

–nvl2函数 假若首个参数为null,则取第两个参数,否则取第二个参数
select nvl2(comm,comm,0) from scott.emp;

–nullif 相等回到null,不等再次回到expr1
select nullif(1,3) from dual;

–多行函数
–case
select * from scott.emp;

select ename,job,sal 基本工资,
case job
when ‘SALESMAN’ THEN sal+sal*0.9
when ‘MANAGER’ THEN sal+sal*0.85
when ‘ANALYST’ THEN sal+100
when ‘CLERK’ THEN sal+200
else sal
end
as 实发工钱 –作为别名
from scott.emp;

–decode函数
select ename,job,sal 基本工资,
decode(job,
‘SALESMAN’, sal+sal*0.39,
‘MANAGER’ , sal+sal*0.85,
‘ANALYST’ , sal+100,
‘CLERK’ , sal+200,
‘PRESIDENT’,sal
)as 实发工钱 –别名
from scott.emp;

–多表连接
create table tb_course(
name varchar2(18),
course varchar2(18),
grade number
);

INSERT INTO tb_course(NAME,course,grade) VALUES(‘tom’,’JDBC’,20);
INSERT INTO tb_course(NAME,course,grade)
VALUES(‘tom’,’Hibernate’,50);
INSERT INTO tb_course(NAME,course,grade) VALUES(‘tom’,’Spring’,80);
INSERT INTO tb_course(NAME,course,grade) VALUES(‘mary’,’JDBC’,30);
INSERT INTO tb_course(NAME,course,grade)
VALUES(‘mary’,’Hibernate’,60);
INSERT INTO tb_course(NAME,course,grade) VALUES(‘mary’,’Spring’,70);

–多表连接1.
select * from tb_course;
select name,grade as JDBC from tb_course where course=’JDBC’;
select name,grade as Hibernate from tb_course where
course=’Hibernate’;
select name,grade as Spring from tb_course where course=’Spring’;

select T4.name,T1.JDBC,T2.Hibernate,T3.Spring
from
(select name,grade as JDBC from tb_course where course=’JDBC’) T1,
(select name,grade as Hibernate from tb_course where
course=’Hibernate’) T2,
(select name,grade as Spring from tb_course where course=’Spring’)
T3,
(select distinct name from tb_course) T4
where T4.name = T1.name and T4.name = T2.name and T4.name = T3.name;

–多表连接2.
select
name,
decode(course,’JDBC’,grade,0) AS
JDBC,–借使’course’列的值是’jdbc’,则显示’grade’的值,否则展现0
decode(course,’Hibernate’,grade,0) AS Hibernate,
decode(course,’Spring’,grade,0) AS Spring
from
tb_course;

–decode(column,value,cloumnvalue,default)
–分组,组函数,decode
select
name,
sum(decode(course,’JDBC’,grade,0)) JDBC,
sum(decode(course,’Hibernate’,grade,0)) Hibernate,
sum(decode(course,’Spring’,grade,0)) Spring
from
tb_course t
GROUP BY t.name;

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