--1
select count (employee_id)
from employees;
--2
select avg(salary)
from pracownicy
where job_id ='IT_PROG';
--3
select count(distinct first_name)
from employees
where first_name like 'A%';
--4
select avg(salary),min(salary),max(salary)
from employees;
--5
select sum(salary), min(salary), max(salary), avg (salary)
from employees
where manager_id is not null;
--6
select sum(salary), job_id
from employees
group by job_id;
--7
select job_id ,count(job_id)
from employees
group by job_id;
--8
select avg(salary), count (employee_id), job_id
from employees
group by job_id
having count (employee_id)>=3;
--9
select first_name, count(first_name)
from employees
group by first_name
having count(first_name)>1
order by count(first_name) desc;
--10
select avg(salary), department_id
from employees
group by department_id
having avg(salary)>9000;
--11
select department_id,min(salary)- max(salary)
from employees
group by department_id;
--12 blad
select menager_id,max(salary)
from employees
group by
order by menager_id;
--13 blad
select department_id, max(salary)
from employees
order by department_id
--14 blad
select count(department_id), department_id,count(distinct department_id)
from employees
group by department_id;
--15
select avg(distinct salary),department_id
from employees
group by department_id;
--16
select max(salary),department_id
from employees
group by department_id
having department_id in (50,60,100);
--17
select min(salary), department_id
from employees
where last_name NOT LIKE '%o%'
group by department_id;
--18
select min(salary),max(salary),department_id
from employees
group by department_id
having count(department_id)<5;
--19
select department_id
from departments
group by department_id
having count (department_id)>1;
--20
select min(hire_date),max(hire_date) department_id
from employees
group by department_id
order by department_id;
--21
select count(employee_id),job_id
from employees
group by  job_id
order by 1 desc;
--22
select count(employee_id),job_id
from employees
group by job_id
having count(job_id)>10;
--23
select count (employee_id), avg(salary), job_id
from employees
where hire_date not between to_date ('01-01-2005', 'dd-mm-yyyy') and to_date ('31-12-2005', 'dd-mm-yyyy')
group by job_id;

--24 blad
select min(salary),menager_id
from employees
group by menager_id;
--25a
select job_id,avg(salary)
from employees
group by job_id
having job_id in ('ST_CLERK','ST_MAN');

--25b
select job_id,avg(salary)
from employees
where job_id in ('ST_CLERK','ST_MAN')
group by job_id;
--26
select max(salary)-min(salary),DEPARTMENT_ID
from employees
where DEPARTMENT_ID in (50,60,100)
group by department_id;
--27
select avg(salary),department_id,
from employees
where department_id in(70,80,110)and  not between hire_date to_date('01-01-2014','dd-mm-yyy')
            and hire_date to_date('31-12-2015','dd-mm-yyy'
  order  by department_id;
--28


  --29

  --30