Context: CREATE TABLE mountain (id VARCHAR, country VARCHAR); CREATE TABLE photos (camera_lens_id VARCHAR, mountain_id VARCHAR)
Question: How many distinct kinds of camera lenses are used to take photos of mountains in the country 'Ethiopia'?
Answer: SELECT COUNT(DISTINCT T2.camera_lens_id) FROM mountain AS T1 JOIN photos AS T2 ON T1.id = T2.mountain_id WHERE T1.country = 'Ethiopia'