创建两个表，一个名为emp，一个名为dept，并且插入数据

create table emp(
empno number(4,0),
ename varchar2(10),
job varchar2(9),
rngr number(4,0),
hiredate date,
sal number(7,2),
comm number(7,2),
deptno number(2,0)
);

create table dept(
deptno number(2,0),
dname varchar2(14 byte),
loc varchar2(13 byte)
);
insert into emp values(7369,'smith','clerk',7902,to_date('1980/12/17','yyyy-mm-dd'),800.00,null,20);
insert into emp values(7499,'allen','salesman',7698,to_date('1981/12/20','yyyy-mm-dd'),1600.00,300.00,30);
insert into emp values(7521,'ward','salesman',7698,to_date('1982/2/22','yyyy-mm-dd'),1250.00,500.00,30);
insert into emp values(7566,'jones','manager',7839,to_date('1981/4/2','yyyy-mm-dd'),2975.00,null,20);
insert into emp values(7654,'martin','manager',7698,to_date('1981/9/28','yyyy-mm-dd'),1250.00,1400.00,30);
insert into emp values(7698,'blake','manager',7839,to_date('1981/5/1','yyyy-mm-dd'),2850.00,null,30);
insert into emp values(7782,'clark','manager',7839,to_date('1981/6/9','yyyy-mm-dd'),2450.00,null,10);
insert into emp values(7788,'scott','analyst',7566,to_date('1987/4/19','yyyy-mm-dd'),3000.00,null,20);
insert into emp values(7839,'king','president',null,to_date('1981/11/17','yyyy-mm-dd'),5000.00,null,10);
insert into emp values(7844,'turner','salesman',7698,to_date('1981/9/8','yyyy-mm-dd'),1500.00,0.00,30);
insert into emp values(7876,'adamas','clerk',7788,to_date('1987/5/23','yyyy-mm-dd'),1100.00,null,20);
insert into emp values(7900,'james','clerk',7698,to_date('1981/12/3','yyyy-mm-dd'),950.00,null,30);
insert into emp values(7902,'ford','analyst',7566,to_date('1981/12/3','yyyy-mm-dd'),1300.00,null,20);
insert into emp values(7934,'miller','clerk',7782,to_date('1982/1/23','yyyy-mm-dd'),1300.00,null,10);

insert into dept values(10,'accounting','new york');
insert into dept values(20,'research','dallas');
insert into dept values(30,'sales','chicago');
insert into dept values(40,'operations','boston');

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--order by:排序.要放在sql语句的最后.  如果有多个需要排序，用逗号隔开。

--asc 升序，desc降序。默认为升序
select *from emp order by sal;
--查看经理的工资排序

select *from emp where job='manager' order by sal;
--查看按照部门排序后的工资排序（升序）

select *from emp order by deptno,sal;
select *from emp;
--部门升序，工资降序排列
select *from emp order by deptno asc,sal desc;
--查看所有员工，并按照入职时间降序排列
select ename from emp order by hiredate desc;
--聚合函数 max/min/sum/avg/count…使用聚合函数时，慎用字段查询。
select max(sal),min(sal),ceil(avg(sal)),count(sal) from emp;
--查看公司平均奖金
select sum(comm),avg(nvl(comm,0)) from emp;

--分组
--查看每个职位的平均薪资
select job,round(avg(sal)) from emp group by job;
--查看平均薪资高于3000的职位
select job,round(avg(sal),2) from emp group by job having avg(sal)>1500;
--在分组中设置条件用having

--内连接a join b on a.x=b.x
select emp.ename ,dept.loc from dept join emp on emp.deptno=dept.deptno;

--外连接 左/右/全 外连接。  left join/right join/ full join左外连接是以左侧为基准(from a join b a为左b为右)，
--即以左侧数据全部显示，若右边没有对应数据则补上null。

--将King的部门号改为50号部门
update emp set deptno=50 where ename='king';
select emp.ename,dept.deptno from emp full join dept on emp.deptno=dept.deptno;

--自连接
select e.ename,e.rngr,m.empno from emp e,emp m where e.rngr=m.empno;

--子查询
--查找和scott同职位的员工 1：知道斯科特啥职位 2：查询这个职位的人
select job from emp where ename='scott';
select ename from emp where job=(select job from emp where ename='scott');

--查询部门中除了salesman之外的人
select ename,deptno from emp where deptno in (select deptno from emp where job='salesman');

--分页查询
select rownum ,ename,job,sal,from emp;

--rownum :从1开始计数，查到一条信息则自增1。
create table empp as
  (select rownum rn,emp.*from emp );
--查看第3-6条数据
select * from empp where rn>3 and rn<6;
drop table empp;
--查看工资排名6-10
select sal from emp;
select * from emp order by sal;
select * from (
    select rownum rn,e.*from(
        select *from emp order by sal) e)
          where rn between 6 and 10;
         

--decode()函数
select ename,job,sal,decode(
job,
'manager',sal*1.2,
'analyst',sal*1.1,
'salesman',sal*1.05,
sal
)de from emp;         --de为别名

--把analyst和manager当做vip，其他的为operation，并计算vip和非vip的人数
select count(*),decode(           --count（）后面+分组函数
job,
'manager','vip',
'analyst','vip',
'operation'
)c from emp group by
decode(
job,
'manager','vip',
'analyst','vip',
'operation'
);