question: How many countries does each continent have? List the continent id, continent name and the number of countries.
#1 return continents 
#2 return countries of  #1 
#3 return number of  #2 for each  #1 
#4 return continent  ids of  #1 
#5 return continent  names of  #1 
#6 return #4 ,  #5 ,   #3