Load only the data that's needed from database with Graphql

I'm learning graphql and I think I've spot one flaw in it. Suppose we have schema like this

type Hero {
  name: String
  friends: [Person]
}

type Person {
  name: String
}

and two queries

{
  hero {
    name
    friends {
      name
    }
  }
}

and this

{
  hero {
    name
  }
}

And a relational database that have two corresponding tables Heros and Persons.

If my understanding is right I can't resolve this queries such that for the first query the resulting sql query would be

select Heros.name, Persons.name
from Heros, Persons
where Hero.name = 'Some' and Persons.heroid = Heros.id

And for the second

select Heros.name, Persons.name from Heros

So that only the fields that are really needed for the query would be loaded from the database.

Am I right about that? Also if graphql would have ability to return only the data that's needed for the query, not the data that's valid for full schema I think this would be possible, right?

In Scala implementation(Sangria-grahlQL) you can achieve this by following:

Suppose this is the client query:

query BookQuery { 
    Books(id:123) { 
      id 
      title 
      author {
        id
        name
      }
    }
}

And this is your QueryType in Garphql Server.

val BooksDataQuery = ObjectType(
    "data_query",
    "Gets books data",
    fields[Repository, Unit](
      Field("Books", ListType(BookType), arguments = bookId :: Nil, resolve = Projector(2, (context, fields) =>{ c.ctx.getBooks(c.arg(bookId), fields).map(res => res)}))
    )
)
val BookType = ObjectType( ....)
val AuthorType = ObjectType( ....)

Repository class:

def getBooks(id: String, projectionFields: Vector[ProjectedName]) {
/* Here you have the list of fields that client specified in the query. 
    in this cse Book's id, title and author - id, name. 
    The fields are nested, for example author has id and name. In this case author will have sequence of id and name. i.e. above query field will look like:
    Vector(ProjectedName(id,Vector()), ProjectedName(title,Vector()),ProjectedName(author,ProjectedName(id,Vector()),ProjectedName(name,Vector())))

    Now you can put your own logic to read and parse fields the collection and make it appropriate for query in database. */
}

So basically, you can intercept specified fields by client in your QueryType's field resolver.