Database: mountain_photos
Question: Show the name and prominence of the mountains whose picture is not taken by a lens of brand 'Sigma'.
SQL: select name ,  prominence from mountain except select t1.name ,  t1.prominence from mountain as t1 join photos as t2 on t1.id  =  t2.mountain_id join camera_lens as t3 on t2.camera_lens_id  =  t3.id where t3.brand  =  'sigma'