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大写
select initcap(‘sql course’) from dual;
–CONCAT 连接两个字符串
select concat(‘Hello’,’World’) from dual;
–substr 取子字符串，从start开始，取count个
select substr(‘HelloWorld’,1,5) from dual;
–substr 取子字符串，从4开始取到末尾
select substr(‘HelloWorld’,-4) from dual;
–LENGTH 返回字符串的长度
select length(‘HelloWorld’) from dual;
–INSTR(string,char) 在一个字符串中搜索指定的字符，返回发现指定的字符的位置，从1开始
select instr(‘HelloWorld’,’o’) from dual;
–RPAD在列的右边粘贴字符，LPAD在列的左边粘贴字符
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 希望被替换的字符或变量
–s1 需要被替换的字符串 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类型的数据
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;
–在日期上加上或减去一个数字结果仍为日期
select sysdate+84 from dual;
–三个转换函数 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;
–不能将非数字的字符串转成number类型
select tb_number(‘abc’) from dual;
–两个日期相减返回日期之间相差的天数
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来向日期中加上或减去小时
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;
–返回d1,d2之间月的数量，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;
–返回日期d加上3个月后的日期，3是整数
select add_months(sysdate,3) from dual;
–返回日期d后第一个星期几的日期
select next_day(sysdate,’星期二’) from dual;
–国外周日是1 ， 所以3指周二
select next_day(sysdate,3) from dual;
–返回d所在月最后一天的日期
select last_day(sysdate) from dual;
–得到下一小时 0分0秒
select trunc(sysdate+1/24,’hh’) from dual;
–得到下一天 0分0秒
select trunc(sysdate+1,’dd’) from dual;
–得到下一月 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 1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 默认按照 dd进行 4舍5入 超过中午 12点就进入下一天
select Round(sysdate) from dual;
–超过15号返回下一个月
select Round(sysdate,’mm’) from dual;
–超过6月就返回下一年1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
–每分钟执行
select trunc(sysdate,’mi’)+1/24/60 from dual;
–每天定时执行3
–例如:每天的凌晨2点执行
select trunc(sysdate)+1+2/24 from dual;
–每周定时执行
–例如：每周一凌晨2点执行
select trunc(next_day(sysdate,2))+2/24 from dual;
–每月定时执行
–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
–例如每季度的第一天凌晨2点执行
select trunc(add_months(sysdate,3),’Q’)+2/24 from dual;
–每半年定时执行
–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1月1日和凌晨2点执行
select add_months(trunc(sysdate,’yyyy’),12)+2/24 from dual;
–通用函数完成一些功能
–nvl函数 如果第一个参数为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，计算年收入
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 如果第一个参数为null，则取第三个参数，否则取第二个参数
select nvl2(comm,comm,0) from scott.emp;
–nullif 相等返回null，不等返回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 实发工资 –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 实发工资 –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,–如果’course’列的值是’jdbc’，则显示’grade’的值，否则显示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;