01． 查询员工表所有数据，并说明使用*的缺点
select * from emp;
01．查询职（job）为'PRESIDENT'的员工的工资
select sal from emp where job='PRESIDENT';
02．查询佣金为0或为null的员工的信息
select * from emp where comm is null or comm=1;
03．查询入职日期在1981-5-1到1981-12-31之间的所有员工的信息
select * from emp where hiredate between to_date(‘1-5月-81’) and to_date(‘31-12月-81’)
04．.查询所有名字长度为4的员工的员工的编号，姓名
select empno,ename from emp where length(ename)=4
05．显示10号部门饿所有经理和20号部门的所有员工
select * from emp where job='MANAGER' and deptno=10 or job='CLERK' and deptno=20;
06．显示姓名没有'L'字的员工的详细信息或含有'SM'字的员工信息
select * from emp where ename not like '%L%' or ename like '%SM%';
07．显示各个部门经理的工资
select deptno,sal from emp where job='MANAGER';
08．显示佣金收入比工资高的员工的详细信息
select * from emp where comm>sal;
10．把hiredate列看做是员工的生日，求本月过生日的员工：
SQL> select * from emp
where to_char(hiredate,'mm')=to_char(sysdate,'mm');
11．把hiredate列看做是员工的生日，求下月过生日的员工
SQL> select * from emp
where to_char(hiredate,'mm')=to_char(add_months(sysdate,1
),'mm');
12.求1982年入职的员工
SQL> select * from emp where to_char(hiredate,'yyyy')='1982';
hiredate是date类型的，1982是字符串类型的，类型匹配才可以
13．求1981年下半年入职的员工
select * from emp
where hiredate between to_date('1981-7-1','yyyy-mm-dd')
and to_date('1982-1-1','yyyy-mm-dd')-1;
注：to_char()函数和to_date()函数
to_char()函数是把日期的类型转换为指定的格式
to_date()是把字符串转换为日期类型
-1的原因是更精确
14．求1981年各个月入职的员工个数
SQL> select to_char(hiredate,'mm'),count(*) from emp where to_char(hiredate,'yyy
y')='1981' group by to_char(hiredate,'mm') order by to_char(hiredate,'mm');
或
select to_char(hiredate,'mm'),count(*) from emp where to_char(hiredate,'yyyy')='1981' group by to_char(hiredate,'mm') order by to_char(hiredate,'mm');
PartII
01 .查询各个部门的平均工资
SQL> select deptno,avg(nvl(sal,0)) from emp group by deptno;
02.显示各种职位的最低工资
SQL> select job,min(sal) from emp group by job;
03．按照入职日期由新到旧排列员工信息
SQL> select hiredate from emp order by hiredate desc;
04．查询员工的基本信息，附加其上级的姓名（自关联）
SQL> select e.*,e1.ename from emp e,emp e1 where e.mgr=e1.empno;
05．显示工资比’ALLEN’高的所有员工的姓名和工作
SQL> select ename,sal from emp where sal>(
select sal from emp where ename='ALLEN');
06．显示与scott从事相同工作的员工的信息（子查询）
SQL> select * from emp where job=(
select job from emp where ename='SCOTT');
07．显示销售部(‘SALES’)员工的姓名
SQL> select e.ename from emp e inner join dept d on e.deptno=d.deptno where d.dname='SALES';
08．显示与30号门’MARTIN’员工工资相同的员工的姓名和工资
SQL> select ename,sal from emp where sal=(select sal from emp where deptno=30 and ename='MARTIN');
09．查询所有工资高于平均工资（包括所有员工）的销售人员
SQL> select * from emp where sal>(
select avg(sal) from emp) and job='SALESMAN';
或
SQL> select * from emp where job='SALESMAN' and sal>(
select avg(sal) from emp);
10．显示所有职员的姓名及其所在部门的名称和工资(表连接)
SQL> select e.*,e.sal,d.dname from emp e inner join dept d on e.deptno=d.deptno;
11．查询在研发部(RESEARCH)工作人员的编号，姓名，工作部门，工作所在地
SQL> select e.empno,e.ename,d.dname,d.loc from emp e inner join dept d on e.deptno=d.deptno where dname='RESEARCH';
12．查询各个部门的名称和员工人数
select e.deptno,d.dname,count(*) from emp e inner join dept d on e.deptno=d.deptno group by e.deptno,d.dname
分析：
SQL> select d.dname from emp e inner join dept d on e.deptno=d.deptno group by e.deptno,d.dname;
DNAME
--------------
ACCOUNTING
RESEARCH
SALES
SQL> select e.deptno,d.dname from emp e inner join dept d on e.deptno=d.deptno group by e.deptno,d.dname;
DEPTNO DNAME
------ --------------
10 ACCOUNTING
20 RESEARCH
30 SALES
SQL> select e.deptno,d.dname,count(*) from emp e inner join dept d on e.d