text: use hr;
  
  select *
  from employees;
  
  select first_name, last_name, 
  concat(first_name, ' - ', last_name)
  from employees
  order by first_name asc, last_name desc;
  
  select first_name, last_name, 
  upper(first_name),
  upper(last_name)
  from employees
  order by last_name desc;
  
  select * 
  from employees
  order by department_id;
  
  select salary, last_name
  from employees
  where salary > 5000
  order by last_name;
  
  select salary
  from employees
  where salary >= 3000 and salary <= 6000
  order by salary asc;
  
  select first_name, phone_number, department_id
   from employees
   where department_id =10 or department_id =30;
   
   
   select  first_name, last_name, hire_date
   from employees
   order by hire_date desc;
   
   select *
   from employees
   where hire_date >='1995-01-01' and hire_date <= '2005-09-20';
   
   select *
   from employees
   where  commission_pct is null  or manager_id is null;
   
   select *
   from employees
   where  commission_pct is not null;
   
   select job_id
   from employees;
   
   
  select * from employees;
  
  
  