create table department (
   departmentid number
  ,departmentdescription varchar2(255)
  ,constraint pk_department primary key(departmentid)
);

create table product (
   productnumber number
  ,productdescription varchar2(255)
  ,productcost number(13,2)
  ,constraint pk_product primary key(productnumber)
);

create table job (
   jobid number
  ,jobdescription varchar2(255)
  ,constraint pk_job primary key(jobid)
);

create table employee (
   empnumber number
  ,empfirstname varchar2(255)
  ,emplastname varchar2(255)
  ,commissionrate number(13,2)
  ,yrlysalary number(13,2)
  ,departmentid number
  ,jobid number
  ,constraint pk_employee primary key(empnumber)
  ,constraint fk_employee_department foreign key (departmentid) references department(departmentid)
  ,constraint fk_employee_job foreign key (jobid) references job(jobid)
);

create table invoice (
   invnumber number
  ,invdate date
  ,empnumber number
  ,invamount number(13,2)
  ,constraint pk_invoide primary key(invnumber)
  ,constraint fk_invoice_employee foreign key (empnumber) references employee(empnumber)
);

create table invoiceline (
   invlinenumber number
  ,invnumber number
  ,productnumber number
  ,quantity number
  ,constraint pk_invoiceline primary key(invnumber,invlinenumber)
  ,constraint fk_invoiceline_invoice foreign key (invnumber) references invoice(invnumber)
  ,constraint fk_invoiceline_product foreign key (productnumber) references product(productnumber)
);

select *
  from employee as a
       inner join department as b
               on b.departmentid=a.departmentid
       inner join invoice as c
               on c.empnumber=a.empnumber
 where b.departmentdescription='Sales'
   and c.invdate between to_date('20121201','YYYYMMDD') and to_date('20121231','YYYYMMDD')