How many countries does each continent have? List the continent id, continent name and the number of countries.
return continents ;return countries of  #1 ;return number of  #2 for each  #1 ;return continent  ids of  #1 ;return continent  names of  #1 ;return #4 ,  #5 ,   #3
['select', 'project', 'group', 'project', 'project', 'union']