Oracle经典20题

--1.列出至少有一个员工的所有部门。select * from dept where deptno in(  select distinct deptno from emp);--2.列出薪金比“SMITH”多的所有员工。select * from emp where sal > (  select distinct sal  from emp where ename = 'SMITH');--3.列出所有员工的姓名及其直接上级的姓名。select a.ename ,b.ename from emp a,emp b where a.mgr = b.empno;--4.列出受雇日期早于其直接上级的所有员工。select a.* from emp a,emp b where a.mgr = b.empno and a.hiredate < b.hiredate;select a.ename ,b.ename from emp a join emp b on a.mgr = b.empno where a.hiredate < b.hiredate;--5.列出部门名称和这些部门的员工信息，同时列出那些没有员工的部门select dept.dname ,emp.* from dept left join emp on dept.deptno = emp.deptno ;--6.列出所有“CLERK”(办事员)的姓名及其部门名称。select ename ,dname from emp,dept where emp.deptno=dept.deptno and job='CLERK'  ; --7.列出最低薪金大于1500的各种工作。select job from emp group by job having min(sal)>1500;--8.列出在部门“SALES”(销售部)工作的员工的姓名，假定不知道销售部的部门编号。select ename from emp where deptno =(  select deptno from dept where dname='SALES');  --9.列出薪金高于公司平均薪金的所有员工。select * from emp  where sal > (  select avg(sal) from emp);  --10.列出与“SCOTT”从事相同工作的所有员工。select  a.ename from emp a,emp b where b.job=a.job and b.ename='SCOTT';select ename from emp where  job=(  select job from emp where ename='SCOTT')  and ename!='SCOTT' ;--11.列出薪金等于部门30中员工的薪金的所有员工的姓名和薪金。select ename ,sal from emp where  deptno!=30 and  sal in (  select sal from emp where deptno=30);--12.列出薪金高于在部门30工作的所有员工的薪金的员工姓名和薪金。select ename ,sal from emp where deptno!=30 and sal >(select min(sal) from emp where deptno=30);--13.列出在每个部门工作的员工数量、平均工资和平均服务期限。trunc(99.9)==99截断函数select count(*) ,trunc(avg(sal)),trunc(avg(sysdate-hiredate)/365) from emp group by deptno;--14.列出所有员工的姓名、部门名称和工资。select emp.ename,dept.dname,emp.sal from emp,dept where emp.deptno = dept.deptno;--15.列出所有部门的详细信息和部门人数。select a.* ,b.num from (select * from  dept) a left join (select deptno,count(*) num from emp group by deptno) b on a.deptno=b.deptno;select dept.deptno,dept.dname,count(*) from dept,emp where dept.deptno=emp.deptno group by dept.deptno,dept.dname ;--16.列出各种工作的最低工资。select job,min(sal) from emp group by job;--17.列出各个部门的MANAGER(经理)的最低薪金。select deptno, min(sal) from emp where job='MANAGER' group by deptno;--18.列出所有员工的年工资,按年薪从低到高排序。select ename,12*(sal) from emp order by sal asc;--19. 求各种工作工资最低的员工select deptno, min(sal) from emp  group by deptno;--20.列出各种工作工资前3名的员工select * from (   select empno,ename,sal,job,dense_rank() over(partition by job order by sal desc) rank from emp ) a   where a.rank<=3   order by job;