Which classroom has the most students?
select classroom from list group by classroom order by count ( * ) desc limit 1
Could you tell me what grade that is, please?
select classroom, grade from list group by classroom order by count ( * ) desc limit 1
What are the first names of the students in that classroom that begin with the letter "S"?
select firstname from list where firstname like " s%" and classroom in ( select classroom from list group by classroom order by count ( * ) desc limit 1 )