//Distinct 
//To eliminate the dulicates in the results.

select distinct(department_id)
from employees  

Example about Upper, Lower, Initcap

select upper(first_name), lower(first_name), initcap(first_name)
from employees 


//RTRIM
//removes the blanks in the strings from the right side 

ITEC212   => 7 chars  
ITEC212--- => 10 chars

select rtrim(course_name)
from courses

//certified_emps
//union     
//it displayes results from both tables with eliminating the duplicates
select first_name, last_name
from employees 
union 
select first_name, last_name
from certified_emps 

//last_name in certified_emps 25 chars   Hunold(25)   rtrim(last_name)  => 6 chars
//last_name in employees without blanks   Hunold(6)                     => 6 chars

select first_name, last_name
from employees 
union 
select first_name, rtrim(last_name)
from certified_emps 


//union all    
//it displayes results from both tables including the duplicates

select first_name, last_name
from employees 
union all
select first_name, rtrim(last_name)
from certified_emps 

//intersect 

select first_name, last_name
from employees 
intersect
select first_name, rtrim(last_name)
from certified_emps 

//minus 
employees - certified_emps 
example 1:
select first_name, last_name
from employees 
minus
select first_name, rtrim(last_name)
from certified_emps 

example 2: 
select first_name, rtrim(last_name)
from certified_emps
minus
select first_name, last_name
from employees