user: Question: What year was the Competition of World Junior Championships with a 20th (qf) position?
Columns: ['Year', 'Competition', 'Venue', 'Position', 'Event', 'Notes']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1999.0, 'African Junior Championships', 'Tunis, Tunisia', '9th (h)', '100 m', '12.60']
SQL:

assistant: SELECT "Year" FROM "Table" WHERE "Competition" = 'World Junior Championships' AND "Position" = '20th (qf)';