先按照发工资排序，工资相同的按照入职日期排序
select ename,job,sal,hiredate from emp order by sal desc,hiredate desc;

　　

查询10部门和20部门下员工信息
	select * from emp where deptno =10 or deptno =20;

　　

一共有几种工作 消除重复行，获取唯一结果
    select distinct job from emp ;

 

查询没有补助的员工信息
    select * from emp where comm is null;
    select * from emp where comm is not null;

--模糊查询姓名中带A的员工信息
    select * from emp where ename like '%A%';
    --第二个字母是A
    select * from emp where ename like '_A%';

    --内容包含'30%'的信息
    select * from emp where ename like '%30\%%' escape '\'

    --区间查询
    select ename,sal from emp where sal >=2000 and sal <=3000;
    select ename,sal from emp where sal between 2000 and 3000;

    --不在区间范围内
    select ename,sal from emp where sal not between 2000 and 3000;
    select ename,sal from emp where sal < 2000 or sal >3000;