create table emp(eid number, ename varchar2(10),age number, salary number);
SELECT*FROM emp;
select count (ename) from emp;
select max (age) from emp;
select min(age) from emp;
select sum(age) from emp;
select avg(age) from emp; 
CREATE VIEW A AS SELECT age FROM emp WHERE age<30;
select * from A;
select salary from emp group by salary;
select ename, salary from emp order by salary;
select ename, salary from emp order by salary desc;
select ename, salary from emp where age<29 group by ename, salary having salary<10000;
create table students(sid int primary key, name varchar(15),login varchar(15), age int, gpa real);
create table Enrolled(sid int, cid int, grade varchar(5),primary key(sid, cid), foreign key (sid) references students (sid));
create view BStudents(name, sid, course) AS SELECT s.name ,s.sid, E.cid from students s,enrolled E where s.sid=e.sid AND E.grade='B';
Drop view Bstudents;