user: Question: Who was the opponent at Ullevi?
Columns: ['Date', 'Venue', 'Opponents', 'Score', 'Comp', 'Attendance']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['2005-04-11', 'Stadion', 'Häcken', '2-1', 'Allsvenskan', '12 823']
SQL:

assistant: SELECT "Opponents" FROM "Table" WHERE "Venue" = 'Ullevi';