---1.分页---
--分页查询台账表T_ACCOUNT，每页10条记录
--查看第一页
select rownum,ac.* from t_account ac where rownum<=10;
select rownum,ac.* from t_account ac where rownum between 1 and 10;
--查看第二页
--rownum：对最终结果集的编号：错误的分页
select rownum,ac.* from t_account ac where rownum between 11 and 20;
--陷入了递归或者无限循环，最终查不出数据：错误的分页
select rownum,ac.* from t_account ac where rownum between 2 and 20;
--正确的分页
select rownum,a.* from
(select rownum mynum,ac.* from t_account ac) a
where a.mynum between 11 and 20;
--------2. 字符函数------------------------
--concat:字符串连接，mysql也是这个函数
--显示emp员工的姓名
--方式一:oracle中连接字符串的符号 ||
select first_name||last_name from emp;
--方式二：concat：连接字符串
select concat(first_name,last_name) from emp;
--initcap:首写字母变大写，其余字母变小写
select initcap('hELLOWoRlD') from dual;--Helloworld
--instr:获取字符首次出现的位置,oracle从1开始计数
select instr('helloworld','l') from dual;--3
--length：长度
select length('helloworld') from dual;--10
--replace：替换
select replace('helloworld','l','@') from dual;--he@@owor@d
--substr:截取字符串
select substr('helloworld',2) from dual;--elloworld
--trim:去除首尾空格
select length(' hello ') from dual;--9
select length(trim(' hello ')) from dual;--5
--lower:全部转小写
select lower('hELLOWoRlD') from dual;--helloworld
--upper:全部转大写
select upper('hELLOWoRlD') from dual;--HELLOWORLD
----------3. 数值函数---------------------
--abs:求绝对值
select abs(-90) from dual;
select abs(90) from dual;
--ceil:进一法
select ceil(90.1) from dual;
select ceil(90.9) from dual;
--floor:去尾法
select floor(90.1) from dual;
select floor(90.9) from dual;
--mod:取模，求余数
select mod(8,3) from dual;
--power:幂次方, 2^3 4^9
select power(2,10) from dual;
--sqrt:开平方
select sqrt(9) from dual;
--round:四舍五入
select round(90.1) from dual;
select round(90.5) from dual;
---------4. 日期函数-----------------
--1 查看系统当前时间
select sysdate from dual;
--2 to_date：构造出一个时间
select to_date('20181203','yyyymmdd') from dual;
select to_date('2018-12-03','yyyy-mm-dd') from dual;
select to_date('2018/12/03','yyyy/mm/dd') from dual;
select to_date('20181203 11:23:36','yyyymmdd hh:mi:ss') from dual;
select to_date('20181203 15:23:36','yyyymmdd hh24:mi:ss') from dual;
--add_months:月份相加
--15个月以后的今天是几月几号？
select add_months(sysdate,15) from dual;
--15个月以前的今天是几月几号?
select add_months(sysdate,-15) from dual;
--15天前的今天是几月几号？
select sysdate-15 from dual;
--15天后的今天是几月几号?
select sysdate+15 from dual;
--last_day:求当前给定日期所在月份的最后一天
--2018年的2月份最后一天的几号？
select last_day(to_date('20180210','yyyymmdd')) from dual;
--2000年的2月份最后一天是几号？
select last_day(to_date('20000210','yyyymmdd')) from dual;
--months_between:日期相减，求月差
select months_between(sysdate,to_date('20000210','yyyymmdd')) from dual;
--求30年之前入职的员工信息
--方式一
select * from emp where add_months(hire_date,12*30) <sysdate;
--方式二
select * from emp where months_between(sysdate,hire_Date)/12>30;
-----------5. 转换函数-----------
--to_char:将日期类型转字符串显示
select to_char(sysdate,'yyyymmdd') from dual;
select to_char(sysdate,'yyyy-mm-dd') from dual;
select to_char(sysdate,'yyyy/mm/dd') from dual;
select to_char(sysdate,'yyyy') from dual;
select to_char(sysdate,'mm') from dual;
select to_char(sysdate,'dd') from dual;
select to_char(sysdate,'hh24') from dual;
select to_char(sysdate,'mi') from dual;
select to_char(sysdate,'ss') from dual;
--to_date(): 字符串转日期
--to_number：将字符串转数值类型
select to_number('10') from dual;
select to_number('10a') from dual;--报错，无法转换
-----------6. 其他函数--------------
--nvl(列，值):当列=null的时候，用值代替
select nvl(manager_id,-100) from emp;
--nvl2(列，列为空的时候的值，列不为空的时候的值)
select nvl2(manager_id,manager_id*10,-100) from emp;
--decode(列,key,value,key,value,key,value)
select decode(ownertypeid,1,'民用电',2,'事业单位用电',3,'商用电') from t_owners;
-----------7. 分析函数---------------
--rank:数值相同排名相同，排名跳跃
select rank() over(order by usenum desc),usenum from t_account;
--dense_rank：数值相同排名相同，排名连续
select dense_rank() over(order by usenum desc),usenum from t_account;
--row_number：不管数值是否相同，排名连续
select row_number() over(order by usenum desc),usenum from t_account;
------------8. 集合操作-------------------------
--并集：
--union all：重复的也显示
select * from t_owners where id <4
union all
select * from t_owners where id <7
--union：虑重
select * from t_owners where id <4
union
select * from t_owners where id <7
--交集 intersect
select * from t_owners where id <4
intersect
select * from t_owners where id <7
--差集
select * from t_owners where id <7
minus
select * from t_owners where id <4
select usenum from t_account order by usenum;
----------8. 视图------------
--创建视图
--创建视图 ：业主类型为1的业主信息
create or replace view v_owners
as
select * from t_owners where ownertypeid = 1;
--查询视图
select * from v_owners;
--
create or replace view v_owners2
as
select id,name,addressid from t_owners where ownertypeid = 1;
--创建视图：查询在海淀区(t_area)的小区名字中含有花园的业主记录(t_owner)(t_address)
create or replace view v_area_address_owner
as
select o.* from t_owners o where o.addressid in
(select id from t_address where name like '%花园%' and areaid in
(select id from t_area where name = '海淀'))
select * from v_area_address_owner;
-----------9. 序列----------
--为student的stuno创建序列
create sequence sq_stuno
start with 1
increment by 2
minvalue 1
maxvalue 999999999
--使用序列
select sq_stuno.nextval from dual;
--插入数据的时候，使用序列作为主键
insert into student values(sq_stuno.nextval,'lucy','lucy@126.com',21,'男',sysdate,'kong',2300,'江苏');
------------------11. 创建索引--------------
--我们经常要根据业主名称搜索业主信息，所以我们基于业主表的name字段来建立索引。
create index index_owner_name on t_owners(name);
select * from student;
select * from t_owners;
