Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.

### Instruction:

Convert text to sql: Count the number of artists who have had volumes. | artist : artist_id , artist , age , famous_title , famous_release_date | volume : volume_id , volume_issue , issue_date , weeks_on_top , song , artist_id | music_festival : id , music_festival , date_of_ceremony , category , volume , result | volume.artist_id = artist.artist_id | music_festival.volume = volume.volume_id | 

### Response:

select count ( distinct _ ) from _ | select count ( distinct artist_id ) from volume