SELECT T1.Name ,  avg(T2.Speed) FROM country AS T1 JOIN roller_coaster AS T2 ON T1.Country_ID  =  T2.Country_ID GROUP BY T1.Name
Show the names of countries and the average speed of roller coasters from each country.
SELECT T1.Name , avg ( T2.Speed ) FROM country AS T1 JOIN roller_coaster AS T2 ON T1.Country_ID = T2.Country_ID GROUP BY T1.Name
select t1 . name , avg ( t2 . speed ) from country as t1 join roller_coaster as t2 on t1 . country_id = t2 . country_id group by t1 . name
Show the names of countries and the average speed of roller coasters from each country .