user: Question: What is the earliest year with less than 45 points for Yamaha team in 21st rank?
Columns: ['Year', 'Class', 'Team', 'Points', 'Rank', 'Wins']
Types: ['real', 'text', 'text', 'real', 'text', 'real']
Sample row: [1969.0, '125cc', 'Maico', 4.0, '40th', 0.0]
SQL:

assistant: SELECT MIN("Year") FROM "Table" WHERE "Points" < 45.0 AND "Team" = 'Yamaha' AND "Rank" = '21st';