user: Question: How many tickets were there sold/available in Barcelona?
Columns: ['Venue', 'City', 'Tickets Sold / Available', 'Gross Revenue (1986)', 'Gross Revenue (2011)']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Råsunda Stadion', 'Stockholm', '37,500 / 37,500 (100%)', '$854,242', '$1,724,333']
SQL:

assistant: SELECT SUM("Tickets Sold / Available") FROM "Table" WHERE "City" = 'Barcelona';