Is it possible to find the size of data contained in a particular query?

e.g.

I can use the following to find the number of rows per date:

select mydatecolumn, count(*) 
from MyTable
where mydatecolumn < '01-JAN-2014'
group by mydatecolumn

But is there a way to find out the size of the data that is contained in those rows?

e.g.

select mydatecolumn, "sizeofactualdata",
from mytable
where mydatecolumn < '01-JAN-2014'
group by mydatecolumn

even if its one query per date that's not a problem.

Is it possible to find the size of data that will be returned by a particular query?

For example, I can use the following to find the number of rows per date:

select mydatecolumn, count(*) 
from MyTable
where mydatecolumn < '01-JAN-2014'
group by mydatecolumn

But is there a way to find out the size of the data that is contained in those rows?

e.g.

select mydatecolumn, "sizeofactualdata",
from mytable
where mydatecolumn < '01-JAN-2014'
group by mydatecolumn

Even if it's one query per date that's not a problem.