create table Department(dName varchar(20),dNumber varchar(10)primary key not null );
create table Employee (name varchar(20),ssn varchar(10) primary key not null,dob date,address varchar(30),sex varchar(6),salary int,dNumber varchar(10) references Department(dNumber) );
create table DepLocation (dNumber varchar(10) references Department(dNumber),dLocation varchar(10),constraint ss primary key(dNumber,dLocation));
create table Project(pName varchar(15),pNumber varchar(10) primary key not null,pLocation varchar(10),dNumber varchar(10) references Department(dNumber));
create table WorksOn(essn varchar(10) references Employee(ssn),pNumber varchar(10)references Project(pNumber),hours int,constraint mm primary key(essn,pNumber));
create table Dependent(essn varchar(10) references Employee(ssn),depName varchar(20),sex varchar(6),dob date,relationship varchar(20),constraint nn primary key(essn,depName));

insert into Department values('graphic','000');
insert into Department values('design','111');
insert into Department values('database','222');
insert into Department values('test','333');

insert into Employee values ('sarah mohmd','1000','3-JAN-1991','mmm st.','female',5000,'333');
insert into Employee values ('sarah sami','2000','8-JUL-1990','kkk st.','female',6000,'111');
insert into Employee values ('hassan','3000','9-JAN-1992','nnn st.','male',3000,'333');
insert into Employee values ('ahmed mohmd','4000','8-JAN-1970','lll st.','male',2000,'000');
insert into Employee values ('miada mohmd','5000','1-JAN-1979','ffff st.','female',5000,'222');

insert into DepLocation values ('000','1 st floor');
insert into DepLocation values ('111','2 nd floor');
insert into DepLocation values ('222','3 rd floor');
insert into DepLocation values ('333','4 th floor');

insert into Project values ('URound','323','building 1','111');
insert into Project values ('simulation','454','building 2','000');
insert into Project values ('phone book','626','building 3','333');
insert into Project values ('battle','727','building 4','222');

insert into WorksOn values ('1000','626',12);
insert into WorksOn values ('2000','323',8);
insert into WorksOn values ('3000','626',10);
insert into WorksOn values ('4000','454',6);
insert into WorksOn values ('5000','727',8);

insert into Dependent values ('1000','test','female','8-JUL-1990','sister');
insert into Dependent values ('2000','dgnesi','male','8-JUL-1990','brother');
insert into Dependent values ('3000','test','female','8-JUL-1997','sister');
insert into Dependent values ('4000','graphic','male','8-JUL-1999','son');
insert into Dependent values ('5000','database','female','8-JUL-1990','sister');

a)
select sum(salary) / sum(hours) from Employee , WorksOn;
b)

c)
 select p.pName from Project p where p.pNumber in (select pNumber from WorksOn having  (min(count(essn)) group by pNumber));

select min(count(essn)) as min_ess from WorksOn group by pNumber;