user: Question: When did the game with North Melbourne as the away team take place?
Columns: ['Home team', 'Home team score', 'Away team', 'Away team score', 'Venue', 'Crowd', 'Date']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'text']
Sample row: ['Footscray', '9.18 (72)', 'North Melbourne', '13.10 (88)', 'Western Oval', 18269.0, '13 April 1968']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Away team" = 'North Melbourne';