user: Question: What's the average number of silver medals when bronze is less than 0?
Columns: ['Rank', 'Nation', 'Gold', 'Silver', 'Bronze', 'Total']
Types: ['real', 'text', 'real', 'real', 'real', 'real']
Sample row: [1.0, 'Ukraine (UKR)', 2.0, 2.0, 0.0, 4.0]
SQL:

assistant: SELECT AVG("Silver") FROM "Table" WHERE "Bronze" < 0.0;