user: Question: What year was the Main role a character named Guan Yu (關羽)?
Columns: ['Year', 'Chinese Title', 'English', 'Role', 'Character']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [2006.0, '屋頂上的綠寶石', 'Emerald on the Roof', 'Minor', 'Nie Kai (聶凱)']
SQL:

assistant: SELECT "Year" FROM "Table" WHERE "Role" = 'Main' AND "Character" = 'Guan Yu (關羽)';