Salgado Sanchez Ivan_Examen2

select tabla1, count()/(select count() from arbol) as proba from arbol where tabla1 in(select distinct tabla1 from arbol) group by tabla1;
select tabla1, tabla2, count()/(select count() from arbol) as proba from arbol where tabla1 in(select distinct tabla1 from arbol) and tabla2 in(select distinct tabla2 from arbol) group by tabla1, tabla1 order by tabla1, tabla2;