user: Question: What is earliest year that had a 50km event with a 2nd place result played in london, united kingdom?
Columns: ['Year', 'Tournament', 'Venue', 'Result', 'Event']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [2001.0, 'World Youth Championships', 'Debrecen , Hungary', '7th', '10,000 m']
SQL:

assistant: SELECT MIN("Year") FROM "Table" WHERE "Event" = '50km' AND "Result" = '2nd' AND "Venue" = 'london, united kingdom';