CREATE TABLE table_name_52 (year_opened INT, main_span_feet VARCHAR, country VARCHAR)

What is the oldest year with a main span feet of 1,640 in South Korea?
SELECT MIN(year_opened) FROM table_name_52 WHERE main_span_feet = "1,640" AND country = "south korea"
SELECT MIN("year_opened") FROM "table_name_52" WHERE "1,640" = "main_span_feet" AND "country" = "south korea"