user: Question: What is the total capacity of venues that opened in 1999?
Columns: ['Metro Vincity', 'Venue Location', 'Address', 'Opened', 'Capacity']
Types: ['text', 'text', 'text', 'text', 'real']
Sample row: ['Greater Boston', 'Harvard Square', '114 Mt Auburn St Cambridge, MA 02138', '1992 (closed in 2003)', 180.0]
SQL:

assistant: SELECT SUM("Capacity") FROM "Table" WHERE "Opened" = '1999';