user: Question: What's the points classification of Stage 18 when the general classification was Denis Menchov?
Columns: ['Stage', 'Winner', 'General classification', 'Points classification', 'Mountains classification', 'Young rider classification']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['1', 'Team Columbia-High Road', 'Mark Cavendish', 'no award', 'no award', 'Mark Cavendish']
SQL:

assistant: SELECT "Points classification" FROM "Table" WHERE "General classification" = 'Denis Menchov' AND "Stage" = '18';