How many released albums are there?
select count ( * ) from albums
How many artists have released albums?
select count ( * ) from artists where id in ( select artist_id from albums )
how many albums are released by artist with 'Led' in their name?
select count ( * ) from artists as t1 join albums as t2 on t1.id = t2.artist_id where t1.name like '%led%'
Show me the names of those albums
select t2.title from artists as t1 join albums as t2 on t1.id = t2.artist_id where t1.name like '%led%'