user: Question: Who is the away side when the crowd is over 18000 with collingwood at home?
Columns: ['Home team', 'Home team score', 'Away team', 'Away team score', 'Venue', 'Crowd', 'Date']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'text']
Sample row: ['Melbourne', '7.13 (55)', 'Richmond', '6.15 (51)', 'MCG', 26558.0, '12 May 1928']
SQL:

assistant: SELECT "Away team" FROM "Table" WHERE "Crowd" > 18000.0 AND "Home team" = 'collingwood';