user: Question: Name the total number of years for USISL Pro League
Columns: ['Year', 'Division', 'League', 'Reg. Season', 'Playoffs', 'Open Cup']
Types: ['real', 'real', 'text', 'text', 'text', 'text']
Sample row: [1994.0, 3.0, 'USISL', '3rd, Northeast', 'Divisional Semifinals', 'Did not enter']
SQL:

assistant: SELECT COUNT("Year") FROM "Table" WHERE "League" = 'USISL Pro League';