Table schema:
CREATE TABLE table_name_50 (diameter__km_ INTEGER, latitude VARCHAR, year_named VARCHAR, longitude VARCHAR)

Question: What is the diameter for 1997 when longitude is 212.0e and latitude is 47.0n?
SQL: SELECT MIN(diameter__km_) FROM table_name_50 WHERE year_named = 1997 AND longitude = "212.0e" AND latitude = "47.0n"