-- Database schema
| roller_coaster : Roller_Coaster_ID [ INT ] primary_key , Name [ TEXT ] , Park [ TEXT ] , Country_ID [ INT ] roller_coaster.Country_ID = country.Country_ID , Length [ INT ] , Height [ INT ] , Speed [ TEXT ] , Opened [ TEXT ] , Status [ TEXT ] | country : Country_ID [ INT ] primary_key , Name [ TEXT ] , Population [ INT ] , Area [ INT ] , Languages [ TEXT ] |
-- -- 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;