user: Question: what is the average silver when the total is more than 20?
Columns: ['Rank', 'Nation', 'Gold', 'Silver', 'Bronze', 'Total']
Types: ['real', 'text', 'real', 'real', 'real', 'real']
Sample row: [1.0, 'Belgium (BEL)', 7.0, 10.0, 3.0, 20.0]
SQL:

assistant: SELECT AVG("Silver") FROM "Table" WHERE "Total" > 20.0;