user: Question: When was the opponent Arsenal?
Columns: ['Date', 'Location', 'Head coach', 'Opponent', 'Result']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['29 July 2008', 'Shah Alam Stadium', 'B. Sathianathan', 'Chelsea', '0–2 (L)']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Opponent" = 'Arsenal';